Chapter 4.7 Trend Analysis Results · Web viewPast trend analyses focused on four parameters: fecal...

CHAPTER 4.7 TREND ANALYSIS RESULTS

Introduction

The Water Quality Monitoring, Restoration, and Information Act (WQMIRA) of the Code of Virginia (§ 62.1-44.19:5.) directs the Department of Environmental Quality (DEQ) to “determine water quality trends within specific and easily identifiable geographically defined water segments…and provide summaries of the trends as well as available data and evaluations so that citizens of the commonwealth can easily interpret and understand the conditions of the geographically defined water segments”1,2. To satisfy this regulatory requirement, the objective of this chapter is to quantify changes in water quality (that is, trends) that have occurred from 1997-2016. In most cases, the 12 chemical and physical water quality characteristics evaluated for this investigation provide a relatively complete description of overall water quality. These characteristics, referred to hereafter as parameters, are included in Table 4.7-1.

Parameter Abbreviation Units Explanation of Units

Chlorophyll a CHLOROPHYLL mg/L Milligrams Chl-A per liter of water

Dissolved Oxygen DOSAT %Saturation Percentage of the saturation concentration of DO at the measured water temperature corrected for Chloride and barometric pressure.

Escherichia coli E. COLI MPN/100mL Most probable number of bacteria in 100mL of water.

Enterococci E. COCCI CFU/100mL Number of colony forming units in 100mL of water.

Fecal coliforms F. COLI CFU/100mL Number of colony forming units in 100mL of water.

Total nitrogen NITROGEN mg/L Milligrams Nitrogen (in all forms) per liter of water.

Total phosphorus PHOSPHORUS mg/L Milligrams Phosphorus (in all forms per liter of water.

pH PH Standard Units The negative log of the hydrogen ion concentration in water.

Specific Conductance

SC µS/cm Amount of conductivity (microSiemens) through 1cm of water.

Total suspended solids

SOLIDS mg/L Milligrams suspended solids per liter of water.

Water temperature TEMPERATURE °C Degrees Celsius

Turbidity TURBIDITY NTU Nephelometric Turbidity Units; a measure of light scattering.

Table 4.7-1 Trend parameters presented in this chapter

Detecting trends requires datasets encompassing longer periods than are traditionally used in the 305(b) assessment process. Furthermore, because of the seasonal variability of water quality parameters, trend datasets must also contain measurements among the various seasons of the year.

1 Trend Analyses of Ambient Water Quality in the Commonwealth of Virginia 1985 – 2005, 2006 Integrated Report, VIRGINIA DEPARTMENT OF ENVIRONMENTAL QUALITY, 2006.

2 CHAPTER 4.5 TREND ANALYSIS, 2012 Integrated Report, VIRGINIA DEPARTMENT OF ENVIRONMENTAL QUALITY, 2012.Draft 2018

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DEQ operates a network of 410 permanent trend stations where monthly or bimonthly data are collected for a variety of key water quality parameters. These fixed stations are located in areas of special interest including those near the mouths of major rivers, along the fall line, near flow gaging stations, or at designated non-tidal stations monitored to evaluate how rivers affect the Chesapeake Bay. These stations have rich histories of monitoring with some dating back to the late 1960s pre-dating the Federal Clean Water Act of 1972 (Figure 4.7-1 and Table 4.7-2).Water quality trends are central to the determination that the efforts of reducing and controlling pollution entering our waters are effective. Water quality trend monitoring may also act as a sentinel to identify new potential risks. The DEQ Statewide Water Quality Monitoring Strategy provides a standardized method for site selection, frequency and methodology of sample collection. This standardization across the trend network provides data that can be statistically analyzed for the detection of water quality trends.

It should be noted that the goal of trend analysis is to detect changes in concentrations or values of key water quality parameters and not on whether the measured values are particularly high or low. For example, an increasing trend in suspended solids indicates degrading water quality, but even after such an increase, solids may remain relatively low and the overall water quality relatively good.

Figure 4.7-1 Water Quality Trend Stations

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WATER QUALITY TREND STATIONS

Sources:1. Trend sites: Virginia Department of Environmental Quality Comprehensive Environmental Data System.2. River Basins: U.S. Environmental Protection Agency BASINS project: https://www.epa.gov/ceam/basins-download-and-installation.

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BASINChesapeake

Chowan

James

New

Potomac

Rappahannock

Roanoke

Shenandoah

Tennesee / Big Sandy

Yadkin

York

STATION TYPE

ESTUARY!ARESERVOIR!ASTREAM!A

MethodsPast trend analyses focused on four parameters: fecal coliform bacteria, total nitrogen, total

phosphorus, and total suspended solids. These variables were selected because together they represent the most common causes of water quality degradation (bacteria, nutrient enrichment, and sedimentation), and the interpretation of changes in their concentrations is generally unambiguous; increasing concentrations are generally interpreted as a degradation in water quality. Sufficient data are now available to allow for trend analysis on eight additional parameters including chlorophyll a, Escherichia coli bacteria (E.coli), Enterococci bacteria, specific conductance, water temperature, turbidity, dissolved oxygen, and pH. These new results add valuable information for the interpretation of improvement or degradation of water quality. Table 4.7-3 lists the total number of stations analyzed by variable.

For the purposes of this chapter, the detection of trends is accomplished by applying a formal statistical analysis to the data. A modified seasonal Kendall analysis developed at the Department of Statistics at Virginia Tech, is used to test the null hypothesis that there is no trend (Zipper et al. 1998). When the test procedure rejects this hypothesis, a measurable trend of increase or decrease has occurred over the period of record. The associated probability, p, indicates the chance of getting the observed results by chance, when no actual trend exists. Therefore, the likelihood that the data indicate an actual trend increases as p decreases. Significant trends are considered at a 90% confidence or greater (p<0.10), that is, when the chance of getting the observed sampling results when no actual change has occurred is less than 10%.

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Table 4.7-2 Long-Term Trend Monitoring Stations (410 total stations) summarized by Water Body Type and Basin.

Basin Water Body Type Number of Stations

Chesapeake*ESTUARY 29

STREAM 5

ChowanESTUARY 7

STREAM 48

JamesESTUARY 46

STREAM 49

PotomacESTUARY 18

STREAM 25

RappahannockESTUARY 16

STREAM 21

NewRESERVOIR 6

STREAM 12

RoanokeRESERVOIR 14

STREAM 43

Shenandoah STREAM 18

Tennessee / Big Sandy STREAM 19

YorkESTUARY 15

STREAM 19

* Chesapeake refers to water bodies in Basin 7 most drain directly into Chesapeake Bay, 7 stations drain directly or indirectly into the Atlantic Ocean.

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Table 4.7-3 Total stations analyzed by parameter. N = total number of individual observations.

Parameter % No Trend % Improving % Degrading Stations N

CHLOROPHYLL 86 12 2 250 20,560

DOSAT 64 28 9 410 59,066

E.COLI 90 2 8 387 29,849

ENTERCOCCI 95 3 2 309 15,385

FECAL COLIFORM 80 18 2 365 49,641

NITROGEN 56 39 5 409 55,644

PH 61 32 7 410 59,456

PHOSPHORUS 85 11 4 365 56,476

SPECIFIC CONDUCTANCE 69 7 24 403 59,877

SOLIDS 72 11 17 408 54,682

TEMPERATURE 82 2 15 410 64,189

TURBIDITY 57 41 2 401 49,504

Statewide trends

Of the 410 monitoring stations included in this study, Figure 4.7-1 and Table 4.7-2, 131 are located in estuaries (that is, water bodies with measurable tidal cycles), 20 are in reservoirs (dammed streams that form artificial lakes), and 259 are in streams (free-flowing fresh waters). Estuary stations are limited to the six easternmost basins that are adjacent to Atlantic Ocean (Chowan Basin) or Chesapeake Bay (waters draining directly to Chesapeake Bay or those in the James, Potomac, Rappahannock or York River Basins). Reservoir stations included here occur in the New River Basin (Claytor Lake) and Roanoke River Basin (Smith Mountain Lake or Lake Gaston). Stream stations occur in 10 major basins, and are the predominant station type in the dataset. This is appropriate because streams are the water body type that covers most of the land area in Virginia. Swamps, isolated ponds and wetlands were not included in this analysis. No trend stations are located in the Yadkin Basin since it occupies only a very small portion in Virginia and consists mostly of small first order streams.

For all 12 parameters analyzed, significant trends were not detected at most sites (i.e. no statistically detectable improvement or degradation was observed from 1997-2016). Chlorophyll, Fecal Coliforms, Nitrogen and Phosphorus showed improving trends at the majority of sites where significant trends were observed. This was not the case for water temperature, where 62 sites showed significant degrading trends (i.e. increasing water temperature) and 9 sites showed improving trends (no significant trends were detected at the remaining 332 sites). This result is consistent with other recent work that has shown an overall increase in water temperatures in the Mid-Atlantic region. Degrading trends in specific conductance also outnumbered improving trends (96 sites showed degrading trends, 29 showed

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improving trends, and the remaining 278 sites showed no significant trend). Specific conductance, that is, the degree to which water conducts electricity, provides an important estimate of the concentration of charged substances (ions) in water, which may indicate pollution. Therefore, the agency has implemented a special study to better evaluate the causes and potential consequences of the observed trends by determining the ions that most contribute to specific conductance. The study is focused on nearly 100 sites where degrading trends have been most rapid or the risks of such degradations appear highest.

E. coli and Enterococci have only been used as bacterial water quality indicators since 2003. Improvements with respect to Enterococci concentrations outnumbered degradations (10 of 309 sites showing improvements versus 5 sites showing degradations), whereas degradations with respect to E. coli outnumbered improvements (32 of 387 sites versus 8 of 387, respectively). It is not known whether the predominance of degrading over improving trends in E. coli, which appeared contradictory to the patterns observed for Fecal coliforms and Enterococci, would have occurred over the entire 20 year period, nor what the cause if this apparent conflict is. Despite this conflict among the bacterial indicators, their general pattern across the trend network was similar, with significant trends being generally rare (e.g. 347 of 387 sites analyzed (90%) showed no significant trends for E. coli).

Turbidity and TSS are generally strongly correlated, and one would expect trends in the two parameters to be to be similar. Improving water quality conditions with respect to turbidity occurred at 168 of 401 sites whereas degrading conditions occurred at only 7 sites. However, degrading conditions for total suspended solids outnumbered improving conditions (70 of 403 site showing improvement vs. 47 sites showing degradation). Many sites that showed degradation with respect to TSS showed improvement with respect to turbidity. The reason for these conflicting results is not known, but may be associated with changes in salinity, which affects turbidity more substantially than TSS.

Dissolved oxygen (DO) increased at 113 of 410 sites and decreased at 36 sites, whereas pH increased at 132 of 410 sites and decreased at 29 sites. Often, pH and DO increases are interpreted as improvements and decreases as degradations, however, many exceptions to this generalization exist for Virginia waters. For example, coastal waters associated with swamps commonly exhibit low pH and DO. Therefore, pH and DO declines in these systems may indicate improvements and increases may indicate degradations. Increases in pH in streams draining karst terrain may indicate increased runoff, and, therefore, degradation.

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Chlorophyll a

Chlorophyll a is the predominant photosynthesizing molecule present in algae and its concentration is a direct measure of the amount of algal biomass present in a waterbody. Increasing algal concentrations are an indication of water quality degradation. Chlorophyll a is measured more often at trend stations in estuaries and reservoirs than in streams. For cost savings, Chlorophyll a is not routinely measured in the Blue Ridge, Valley and Ridge, and Allegheny Plateau Physiographic Provinces because values have been historically low here.

Overall chlorophyll a improved between 1997 and 2016. Of the 250 stations analyzed 30 (12 percent) showed significant improvement (Table 4.7-5 and Figure 4.7-4). Most improvements occurred in the Chesapeake Bay Basin although improving conditions outnumbered degrading conditions in all of the major river basins. In 5 of 10 Virginia River Basins (Chesapeake, Chowan, New, Shenandoah and Tennessee River Basins) no degrading trends in chlorophyll a were detected (Table 4.7-6).

Table 4.7-4 Percentage of stations statewide exhibiting no statistically significant trend, improving (decreasing) Chlorophyll a and degrading (increasing) Chlorophyll a.

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Stations # of Samples % Improving % Degrading % No Trend

250 20,560 12 2 86

Figure 4.7-2 Statewide trends in Chlorophyll a

Table 4.7-5 Chlorophyll a: basinwide summary. Numbers indicate number of monitoring stations where improving (decreased Chlorophyll a) or degrading (increased Chlorophyll a) trends were

detected.

Basin Improving Degrading No TrendChesapeake* 13 0 16Chowan 0 0 39James 6 1 60New 2 0 8Potomac 5 1 23Rappahannock 2 1 14Roanoke 2 1 22Shenandoah 0 0 4Tennessee / Big Sandy 0 0 13York 0 1 16


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0 110 22055 Miles

WATER QUALITY TRENDS 1997 through 2016

BASINChesapeake

Chowan

James

New

Potomac

Rappahannock

Roanoke

Shenandoah


Yadkin

York

Chlorophyll TrendsDEGRADING (Chlorophyll increasing)

IMPROVING (Chlorophyll decreasing)

NO TREND

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BacteriaHumans and warm-blooded animals harbor large numbers of bacteria, including fecal coliforms,

enterococci, and Escherichia coli (E. coli) in their intestinal tracts. Their presence in water is an indicator of contamination from untreated human sewage or animal feces (i.e. fecal contamination). Major sources of fecal contamination are direct discharge of untreated human sewage, storm water runoff, leaking sewer lines, concentrated animal feeding operations (CAFOs), farms, domestic pets, and wildlife. Prior to the summer of 2003, fecal coliforms were used for bacteria monitoring. Since then, human health-related bacteria water quality standards have transitioned to E. coli in fresh waters and Enterococci in salt water (see Virginia Code; 9VAC25-260-170-A). The units of fecal coliforms and Enterococci are expressed as number of colonies per 100mL of sample (CFU/100mL) and E. coli have been expressed as most probable number of bacteria per 100mL of sample (MPN/100mL) as well as CFU/100mL, depending on the specific methodology used. The two E. coli unit types are equivalent within the concentration range analyzed here.

Although Water Quality Standards for fecal coliforms have been replaced with E. coli for freshwater and Enterococci, for saltwater, the fecal coliform group of bacteria remains a useful indicator of water quality conditions. The fecal coliform record extends back almost 4 decades and will continue to serve as an indicator for water quality trends.

Fecal Coliform improved at 66 (18 percent) stations, and degraded at 7 (2 percent) stations, 6 of these 7 stations had no detectable slope (Table 4.7-7 and Figure 4.7-5) meaning the change although statistically significant was minimal, with no clear effect on water quality.

E.coli trends were calculated for 387 stations. Eight stations (2 percent of stations) showed improvement with discernable slopes. Of the 32 stations (9 percent) with degrading conditions only 7 (2 percent) had slopes that were above detection, with a range of 0.7 CFU yr-1 to 16 CFU yr-1 (Table 4.7-7 and Figure 4.7-6).

Enterococci trends were calculated for 309 stations of which 95 percent had no measureable trend (Table 4.7-7 and Figure 4.7-7). Of those stations with statistically significant trends 4 of 5 stations had measurable and positive slopes, which ranged from 4 CFU yr-1 to 13 CFU yr-1 (considered degrading water quality).

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Parameter Stations # of Samples % Improving % Degrading % No Trend

Fecal Coliform 365 49,641 18 2 80

E. coli 387 29,849 2 9 89

Enterococci 309 15,385 3 2 95

Table 4.7-6 Percentage of stations statewide exhibiting no statistically significant trend, improving (decreasing) bacteria and degrading (increasing) bacteria.

Figure 4.7-3 Statewide trends in Fecal Coliform

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0 110 22055 Miles


BASINChesapeake

Chowan

James

New

Potomac

Rappahannock

Roanoke

Shenandoah


Yadkin

York

!.

Fecal Coliform TrendsDEGRADING (coliforms increasing)

IMPROVING (coliforms decreasing)

NO TREND

#*#*!

Figure 4.7-4 Statewide trends in E. coli

Figure 4.7-5 Statewide trends in Enterococci

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0 110 22055 Miles


BASINChesapeake

Chowan

James

New

Potomac

Rappahannock

Roanoke

Shenandoah


Yadkin

York

!.

E. coli TrendsDEGRADING (E. coli increasing)

IMPROVING (E. coli decreasing)

NO TREND

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.

0 110 22055 Miles


BASINChesapeake

Chowan

James

New

Potomac

Rappahannock

Roanoke

Shenandoah


Yadkin

York

Enterococci TrendsDEGRADING (Enterococci increasing)

IMPROVING (Enterococci decreasing)

NO TREND

#*#*

!

Table 4.7-7 Bacteria: basinwide summary. Numbers indicate number of monitoring stations where improving (decreased bacteria) or degrading (increased bacteria) were detected.

Fecal Coliform E. coli Enterococci

Basin Improving Degrading No Trend

Improving Degrading

No Trend

Improving Degrading No Trend

Chesapeake* 11 1 22 0 2 32 1 1 32

Chowan 6 1 47 0 5 44 1 0 45

James 21 5 61 1 13 78 3 1 76

New 0 0 12 0 2 16 0 0 6

Potomac 3 0 37 0 2 39 1 0 30

Rappahannock 9 0 24 1 0 31 0 1 30

Roanoke 6 1 33 5 5 42 0 0 27

Shenandoah 6 0 12 1 2 15 1 0 14

Tennessee/Big Sandy

1 0 16 0 0 17 0 1 12

York 3 0 27 0 1 33 3 1 22


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174

Total NitrogenNitrogen is an essential element to all life forms including aquatic plants and algae. Although

some nitrogen is required to support plant and animal life in healthy lakes, streams and estuaries, an excess of nitrogen is an indication of nutrient enrichment, an undesirable water quality characteristic. Nutrient enrichment often accelerates algae and plant growth (a process called eutrophication). The algae, in particular, may decompose rapidly, consuming more dissolved oxygen than can be replaced in the water and suffocating aquatic life. In addition, algal blooms may produce toxins which harm aquatic life and endanger human health. Nitrogen enters the watershed from several main sources, 1) atmospheric deposition mainly from oxides of nitrogen produced during combustion of fossil fuels, 2) wastewater treatment plants, 3) urban and suburban storm water runoff, 4) concentrated animal feeding operations (CAFO), and 5) agriculture.

A decrease in concentration of total nitrogen over time is considered an improvement in the watershed. Improving water quality nitrogen trends were detected at 159 stations (Table 4.7-9 and Figure 4.7-8) with most of the improvements occurring in the Chesapeake, James, Chowan, Potomac and Rappahannock basins (Table 4.7-10). Degrading water quality for Nitrogen occurred at 20 stations in 8 or the 10 major river basins. The most occur in the Roanoke River basin, which drains to the Albemarle Sound.

Table 4.7-8 Percentage of stations statewide exhibiting no statistically significant trend, improving (decreasing) total nitrogen and degrading (increasing) total nitrogen.

Draft 2018

175


409 55,644 39 5 56

Figure 4.7-6 Statewide trends in Total Nitrogen

Table 4.7-9 Total Nitrogen: basinwide summary. Numbers indicate number of monitoring stations where improving (decreased nitrogen) or degrading (increased nitrogen) were detected.

Basin Improving Degrading No Trend

Chesapeake* 26 0 8

Chowan 20 2 33

James 34 3 57

New 2 1 15

Potomac 28 0 15

Rappahannock 17 1 19

Roanoke 16 6 35

Shenandoah 6 3 9

Tennessee / Big Sandy 2 3 14

York 8 1 25


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176

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.

0 110 22055 Miles


BASINChesapeake

Chowan

James

New

Potomac

Rappahannock

Roanoke

Shenandoah


Yadkin

York

Nitrogen TrendsDEGRADING (nitrogen increasing)

IMPROVING (nitrogen decreasing)

! NO TREND

#*

#*

Total PhosphorusPhosphorus like nitrogen is essential to all life. Phosphorus enrichment may also lead to

eutrophication, dissolved oxygen depletion and proliferation of algae that may adversely affect human health. Phosphorus generally enters waterways as phosphate (PO4), which may be in the form of orthophosphate (PO4 molecules alone), organic phosphate, (PO4 attached to organic chemicals such as proteins or carbohydrates) or condensed inorganic phosphate (PO4 attached to inorganic chemicals). Sources of phosphorus to Virginia waterways are similar to nitrogen, except that little phosphorus input occurs from the atmosphere.

Phosphorus concentrations remained low during the time period of this study. Of the 365 stations analyzed, no trends were detected at 311 stations (85 percent), improving conditions (decreasing phosphorus concentrations) were detected at 39 stations (11 percent) and degrading conditions were detected at 15 sites (Table 4.7-11 and Figure 4.7-9).

Of the 15 stations where degrading conditions were detected, 12 occurred in a cluster in the Chowan River Basin, and 6 of these occurred along an approximately 5-mile stretch of the Northwest River (near Chesapeake, VA (Table 4.7-12). The 2 stations with degrading trends not located in the Chowan River Basin were a station on the South Anna River in Louisa County (Piedmont region in central Virginia) and a station on an unnamed tributary of Pitts Creek in Accomack County.

Table 4.7-10: Percentage of stations statewide exhibiting no significant trend (p> 0.10), improving (decreasing) total phosphorus and degrading (increasing) total phosphorus.

Draft 2018

177


365 56,476 11 4 85

Figure 4.7-7 Statewide trends in Total Phosphorus

Table 4.7-11 Total Phosphorous: basinwide summary. Numbers indicate number of monitoring stations where improving (decreased phosphorous) or degrading (increased phosphorous) were

detected.



Specific Conductance

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178

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.

0 110 22055 Miles


BASINChesapeake

Chowan

James

New

Potomac

Rappahannock

Roanoke

Shenandoah


Yadkin

York

!.

Phosphorus TrendsDEGRADING (Phosphorus increasing)

IMPROVING (Phosphorus decreasing)

NO TREND

#*#*

!

Specific conductance (SC) is a measure of how much electricity is transmitted through water. SC is measured in the field and reported as uS cm-1 corrected to a standard temperature of 25 C because increased temperature increases conductivity. In freshwater, increasing SC can be a sign of increasing pollution. SC is affected by the concentration of major ions in solution that may include the anions of Sulfate, Chloride, Phosphate, Nitrate and the cations of Sodium, Potassium, Magnesium, Calcium, Aluminum, and Iron. The mobility of and the oxidation state of these ions will influence SC measurements as well a temperature. Prior to 1985, Specific Conductivity was reported which is the equivalent to SC without a temperature correction to 25 C.

Of the 12 variables analyzed for this report, SC had the largest percentage of degrading conditions reported at 93 stations (23 percent) (Table 4.7-13 and Figure 4.7-10). The mean increase among stations with an increasing trend was of 80 uS cm-1.

The largest numbers of degrading trends were seen in the Roanoke and Potomac River basins. The Chowan River basin has the greatest number of improving trends at 15 stations and no degrading trends during the study period (Table 4.7-14).

Because of the magnitude and wide geographic distribution of the increasing trends in conductivity, which has occurred in both urban and rural streams approximately, nearly 100 stations have been targeted to include additional major ion monitoring. Monitoring to identify the major constituents contributing to the increases in SC3 will continue as part of a long-term strategy to further quantify the causes for the rates of change in SC.

Table 4.7-12: Percentage of stations statewide exhibiting no significant trend (p> 0.10), improving (decreasing) specific conductance and degrading (increasing) specific conductance.


403 59,877 7 24 69

3 Parametric Coverage at Trend Stations, Ions, TREND_IONS.docx.Draft 2018

179

Figure 4.7-8 Statewide trends in Specific Conductance

Table 4.7-13 Specific Conductance: basinwide summary. Numbers indicate number of monitoring stations where improving (decreased specific conductivity) or degrading (increased specific

conductivity) were detected.



Surface Water Temperature

Draft 2018

180

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.

0 110 22055 Miles


BASINChesapeake

Chowan

James

New

Potomac

Rappahannock

Roanoke

Shenandoah


Yadkin

York

!.

Specific conductance (SC) TrendsDEGRADING (SC increasing)

IMPROVING (SC decreasing)

NO TREND

#*#*

!

An appropriate temperature range is important to sustaining aquatic life. Temperature has an influence on regulating respiration rates, spawning, and the maximum concentration of dissolved oxygen in solution with the ambient water (increasing temperature reduces DO and therefore may limit respiration). In addition, animals and plants under thermal stress from abnormally high water temperatures are at increased risk of adverse effects from other pollutants. Temperature standards exist for “the propagation and growth of a balanced indigenous population of aquatic life” as described in the clean water act (33 U.S.C. §1251 et seq; this is, more correctly, a balanced and indigenous community of aquatic life). Pollution events that cause harm to aquatic communities via water cooling are extremely rare in VA, and not known to exist at the stations in the trend network. Therefore, increasing trends in water temperature are considered degradation, and decreases in temperature are considered improvements.

Most stations (82 percent) showed no trend in water temperature (Table 4.7-15 and Figure 4.7-11). Surface water temperature in degrees Celsius, oC, increased at 63 stations. Many of these increases were clustered at reservoir sites around Smith Mountain Lake in the Roanoke basin, estuary sites on the mainstem of the York and Rappahannock Rivers and streams and estuaries in the Chowan Basin (Table 4.7-16).

Table 4.7-14 Percentage of stations statewide exhibiting no statistically significant trend, improving (decreasing temperature) and degrading (increasing temperature).

Draft 2018

181


410 64,189 2 15 82

Figure 4.7-9 Statewide trends in Surface Water Temperature

Table 4.7-15 Surface water temperature: basinwide summary. Numbers indicate number of monitoring stations where improving (decreased temperature) or degrading (increased

temperature) were detected.



Draft 2018

182

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.

0 110 22055 Miles


BASINChesapeake

Chowan

James

New

Potomac

Rappahannock

Roanoke

Shenandoah


Yadkin

York

!.

Temperature TrendsDEGRADING (temp. increasing)

IMPROVING (temp. decreasing)

NO TREND

#*#*

!

Water Clarity, TurbidityTurbidity is a measure of water clarity and is determined by detecting the amount of light that is

scattered through the water. The more light that is scattered the cloudier the water and therefore the more turbid. The more turbid the water the less light is available to photosynthesizing organisms, an indication of poorer water quality. Decreasing turbidity values generally indicate water quality improvement. Particles that affect turbidity may include algae, bacteria, organic and inorganic suspended solids. Not all light scattering particles are visible to the naked eye. In surface waters, turbidity primarily increases with increases in plankton and suspended solids and, therefore, increased turbidity is often an indicator of excessive erosion and runoff from the land surface or of nutrient pollution Turbidity is measured at the surface from samples collected at 1 meter or less.

Overall water clarity, as measured by turbidity, improved between 1997 and 2016. Of the 408 stations analyzed 168 (41 percent) showed significant improvement. Most improvements occurred in the Chesapeake Bay and the Albemarle Sound Basins although improving conditions outnumbered degrading conditions in all of the major river basins. In 6 of 10 Virginia River Basins (Albemarle Sound and the New, Potomac, Rappahannock, Shenandoah and Tennessee River Basins) no degrading trends in turbidity were detected (Table 4.7-18).

Table 4.7-16 Percentage of stations statewide exhibiting no statistically significant trend, improving water clarity (decreasing turbidity) and degrading water clarity (increasing turbidity).

Draft 2018

183


401 49,504 41 2 57

Figure 4.7-10 Statewide trends in water clarity as measured by Turbidity

Table 4.7-17 Water clarity as measured by turbidity: basinwide summary. Numbers indicate number of monitoring stations where improving (decreased turbidity) or degrading (increased

turbidity) were detected.



Total Suspended SolidsTotal suspended solids (TSS or SOLIDS) is a measure of the concentration of solids suspended

Draft 2018

184

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.

0 110 22055 Miles


BASINChesapeake

Chowan

James

New

Potomac

Rappahannock

Roanoke

Shenandoah


Yadkin

York

Turbidity TrendsDEGRADING (turbidity increasing)

IMPROVING (turbidity decreasing)

!. NO TREND

#*#*

!

in the water column. Although a water quality standard or screening value does not exist for TSS it is an important water quality driving parameter for several reasons. TSS can serve as an indicator of excessive water column sediment, which can cause habitat destruction, which harms aquatic animals, plants and algae. Excessive sedimentation can also transport toxic organics, metals, and excessive phosphorus loads. Excess TSS in the water column blocks sunlight, which is necessary for the propagation of submerged aquatic vegetation.

Sources of TSS vary with the most significant being from construction sites, land clearing activities and unregulated silviculture. Other potential sources of TSS are agricultural runoff, storm water runoff, and stream bank erosion.

Suspended solids are rarely composed of homogenous particles. They vary in size and composition and can represent a complex mixture of a diverse range of organic and inorganic substances. The same particles that affect water clarity (i.e. Turbidity) may also contribute to the TSS fraction in the water column and may include algae, bacteria, organic and inorganic species, and colloidal compounds (microscopic suspended particles).

Most stations (72 percent) showed no trend in total suspended solids (Table 4.7-19 and Figure 4.7-13). TSS concentrations increased at 70 stations. Many of these increases were seen at estuarine sites with improving trends for turbidity, total nitrogen and chlorophyll a (Table 4.7-16). Further analysis and sampling are needed to determine the cause of these trend results.

Table 4.7-18 Percentage of stations statewide exhibiting no statistically significant trend, improving (decreasing TSS concentration) and degrading (increasing TSS concentration).

Draft 2018

185


408 54,682 11 17 72

Figure 4.7-11 Statewide trends in Total Suspended Solids

Table 4.7-19 Total suspended solids: basinwide summary. Numbers indicate number of monitoring stations where improving (decreased TSS concentrations) or degrading (increased

TSS concentrations) were detected.



Draft 2018

186

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Dissolved Oxygen & pH

Dissolved oxygen (DO) exhibited significant increasing trends at 113 of 410 sites and significant decreasing trends at 36 sites, whereas pH exhibited significant increasing trends at 132 of 410 sites and significant decreasing at 29 sites (Seasonal Kendall analysis; p<0.10). Further investigation is needed to determine the meaning of these changes for water quality. In some systems, increases in DO and pH indicate water quality improvements; however, many exceptions to this generalization exist for Virginia waters. For example, coastal waters associated with swamps commonly exhibit low pH and DO. Therefore, pH and DO declines in these systems may indicate improvements and increases may indicate degradations. As a second example, increases in pH in streams draining limestone areas may indicate increased runoff, and, therefore, degradation. A thorough evaluation of the other water quality trends presented here, as well as the study on specific ions discussed previously, are being conducted in order to better understand what the observed trends in DO and pH mean for water quality at each station.

Stream Flow & Flow Adjusted Trends

In addition to the concentration of materials in the water column, water flow (amount of water per unit time) is important when evaluating trends. Flow (more specifically referred to as discharge) is expressed as the volume of water passing a given point over a given time period (e.g. cubic meters per second). Discharge may increase the effects of a given pollutant, by allowing a water body to carry more material, or may decrease its effects by dilution. From 1997-2016, precipitation exceeded historical averages in most months (Figure 4.7-14). The effects of discharge on water quality are likely to be greatest in high-precipitation periods such as this, when discharge is increased.

Results thus far have been presented without considering flow. For example, the trends reported for total suspended solids (TSS) describe increases or decreases in the concentration of TSS in the water (milligrams TSS per liter of water). However, at the same concentration, more TSS would be carried by a water body if flow were increased. The total amount of material carried by a water body is commonly referred to as its load. Loads are important for evaluating the effects of a tributary stream or river on the receiving water body. For example, increased loads of TSS, nitrogen and phosphorus delivered by rivers to Chesapeake Bay negatively affect the health of the bay. Whereas loads may be important for downstream waters, concentrations of TSS, nitrogen and phosphorus (as report in previous sections) are more important for affecting in the water body where the measurements were taken.

Based on the importance of evaluating flows and loads in addition to concentrations, DEQ has begun to expand the trend analysis to include flow-adjusted trends to take into account the effects of discharge on each parameter. Initial analyses have been focused on nitrogen, phosphorus, and TSS, as these substances are of primary interest for water quality in Chesapeake Bay. These analyses should provide information on the overall amount nitrogen, phosphorus and TSS transported to downstream water bodies from trend sites, as well as the overall effects that changing hydrology can have on water quality in the commonwealth. Because these analyses are in development, presentation and interpretation of the results are beyond the scope of this chapter.

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ConclusionIn the last 20 years, the commonwealth has added 1.6 million people to the resident population,

23 percent (Figure 4.7-15), and between 2004 and 2016 (for which data exist) approximately 840,000 single resident (equivalents) building permits4 were issued. Given this substantial increase in population, and that water quality improvements outnumbered degradations by a factor of 2 to 1, and the number of no trends outnumbered degrading trends greater than 8 to 1, it is an encouraging indication that water quality in the commonwealth seems to be stable and possibly improving.

Figure 4.7-12 Virginia Resident Population

The largest improvements in water quality over the past 20 years are for Water Clarity, Nitrogen, Phosphorus, Fecal Coliform, and Chlorophyll. We consider these trends a success story. The efforts of the last 20 years have been to control nutrients and bacteria; both water clarity and chlorophyll are indicator variables whose trends support the reduction in nutrients and bacteria. Considering all stations for all parameters 18 percent of the 4500+ individual analyses, not including flow adjusted analyses, exhibited improving water quality conditions. Only 9 percent indicated declining water quality conditions, primarily in surface water temperature, specific conductance, and total suspended solids. Improving and no changes in water quality together account for 91 percent of the approximately 50,000 to 60,000 individual measurements taken at more than 400 stations over the 20-year span.

With the identification of significant degrading conditions of Specific Conductance (SC), a plan of action has been initiated to conduct long term monitoring of the major anions and cations at a subset of those most affected stations. The results of these additional parameters will be to identify the source of SC degradation to assist with future control strategies.

4 U.S. Census Bureau.Draft 2018

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1997

2000

2003

2006

2009

2012

20156.50

8.50

Virginia resident population in mil-

lions, 23% increase

ReferencesZipper, C.E., G. Holtzman, P. Darken, P. Thomas, J. Gildea, and T. Younos. 1998. Long-Term Water Quality Trends in Virginia’s Waterways. VWRRC Special Report No. SR11-1998. December

1998. Virginia Water Resources Research Center, Blacksburg, Va. http://hdl.handle.net/10919/49457 (accessed November 7, 2018)

Oelsner, G.P., Sprague, L.A., Murphy, J.C., Zuellig, R.E., Johnson, H.M., Ryberg, K.R., Falcone, J.A., Stets, E.G., Vec-chia, A.V., Riskin, M.L., De Cicco, L.A., Mills, T.J., and Farmer, W.H., 2017, Water-quality trends in the Nation’s rivers and streams, 1972–2012—Data preparation, statistical methods, and trend results (ver. 2.0, October 2017): U.S. Geological Survey Scientific Investigations Report 2017–5006. Available at: https://doi.org/10.3133/sir20175006 (accessed Aug. 16, 2018).

Moyer, D.L. and Blomquist, J.D., 2018, Nitrogen, phosphorus, and suspended-sediment loads and trends measured at the Chesapeake Bay River Input Monitoring stations: Water years 1985-2017, U.S. Geological Survey data release. Available at: https://doi.org/10.5066/P96NUK3Q (accessed Aug. 6, 2018).

Dauer, D. M., Egerton, T.A., Donat, J. R., Lane, M. F., Doughten, S. C., Johnson, C. and Arora, M. 2008. Current status and long-term trends in water quality and living resources in the Virginia tributaries and Chesapeake Bay mainstem from 1985 through 2015. Available at: http://www.sci.odu.edu/chesapeakebay/reports/trends/2015/VA_Basin_Summary_2015_Final_01_31_2017.pdf . (accessed Aug. 6, 2018)

Virginia Department of Environmental Quality. 2006. Trend Analyses of Ambient Water Quality in the Commonwealth of Virginia 1985 – 2005, 2006 Integrated Report.

Virginia Department of Environmental Quality. 2012. Chapter 4.5 Trend Analysis, 2012 Integrated Report.

Commonwealth of Virginia. June 5, 2017. Water Quality Standards (9 VAC 25-260-00 et seq.). Department of Environmental Quality, Richmond, VA. https://law.lis.virginia.gov/admincode/title9/agency25/chapter260/

Kaushal, S.S., et.al., Freshwater salinization syndrome on a continental scale, PNAS, Published online January 8, 2018, www.pnas.org/cgi/doi/10.1073/pnas.1711234115

Lefcheck, Jonathan S. et.al, Multiple stressors threaten the imperiled coastal foundation species eelgrass (Zostera marina) in Chesapeake Bay, USA, Global Change Biology (2017), doi: 10.1111/gcb.13623.

SAS Institute Inc. 2008. SAS/STAT® 9.2 User’s Guide. Cary, NC: SAS Institute Inc.

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