Nutrients & Algal Blooms Developing water quality standards for the James River.

Transcription

1 Nutrients & Algal Blooms Developing water quality standards for the James River. Dr. Paul A. Bukaveckas and Dr. Joseph Wood Department of Biology Center for Environmental Studies

2 Algal Blooms in the James Richmond VCU Rice Center region of chronic algal blooms region of periodic dinoflagellate blooms Data from DEQ CBP monitoring ( )

3 Algal Blooms in the James: Why here? Sampling locations for VCU weekly monitoring (2010-present). Persistent blooms occur in the region where the James transitions from a narrow, deep channel to a wide shallow channel. Shallow areas provide more favorable light conditions which enhance algal growth.

4 Why Here? Depth effects on Light Availability Channel form: near Richmond Channel form: near Hopewell photic zone depth = 1-4 m depth = 4-8 m Release from light limitation and longer water residence time allows greater nutrient utilization by algae.

5 Why here? Nutrient Sources to James TN Load (kg/d) TP Load (kg/d) Local Point Sources Upper Watershed 0 Annual Summer 0 Annual Summer Data are average values for Point Sources (PS) include WWTPs, Industry and Richmond CSOs. Summer = May - September

6 Algal Blooms in the James River Key Questions Where/when/why do algal blooms occur? What are the deleterious effects of algal blooms? Fixing the problem: How do we determine what is an acceptable nutrient load? 6-year project funded by Virginia. Collaborative effort: DEQ, VCU, ODU and VIMS. Data collection & modeling.

7 Impairments Arising from Algal Blooms Water quality low dissolved oxygen: chronic depletion (hypoxia) in deep waters; transient (night-time) minima elevated ph: daytime maxima during blooms Water Clarity: algal contributions to suspended particulate matter Algal Toxins: effects on aquatic biota and concerns for human health

8 Dissolved Oxygen Continuous (15 min) monitoring at VCU Rice Center Research Pier (2013)

9 Effects of Algal Blooms on Water Quality Probability of impairment in relation to CHLa. DO (nighttime minima) and ph (daytime maxima) data are from continuous monitoring. CHLa is from weekly monitoring.

10 Effects of Algal Blooms on Water Clarity Algal contributions to suspended particulate matter (TSS) shown as probability of exceeding specified threshold values.

11 Harmful Algal Blooms Certain types of algae produce chemical defense compounds (phytotoxins). In freshwaters, the most common are cyanotoxins produced by blue-green algae. Toxins enter the food chain resulting in wildlife and human health concerns. In late summer, algal blooms in the James are dominated by cyanobacteria including known toxinproducing species (Microcystis).

12 Harmful Algal Blooms in the James 10-May 31-May 21-Jun 12-Jul 2-Aug 23-Aug 13-Sep CHLa (ug/l) CHLa Microcystin Microcystin (ug/l) Contact standard Drinking standard* 10-May 9-Jun 9-Jul 8-Aug 7-Sep CHLa and cyanotoxins in the James River during *for treated water

13 Cyanobacteria Blooms in the James From: Wood et al. (2014) ES&T

14 Microcystin in the Food Web of the James

15 Microcystin in the Food Web Why are some taxa more vulnerable than others? Liver Microcystin (µg ḡ 1 DM Liver) Blue Catfish (0-20 cm) (20-40 cm) Gizzard Shad (adult) Atlantic Menhaden Threadfin Shad Gizzard Shad YOY R 2 = CHLa (µg g -1 DM stomach contents) Fish that feed in the water column ingest more algae, and more toxin, then those feeding on the bottom.

16 Assessing Water Quality Standards Are current CHLa standards for the James protective of designated uses (aquatic life, etc.)? What is the likelihood of impairment at a given CHLa concentration? What is the likelihood of exceeding that CHLa concentration if current CHLa standard is attained?

17 Assessing Risk of Impairment Current CHLa standard for tidal fresh = 23 µg/l (Jul-Sep mean)

18 Funding provided by VA DEQ and City of Richmond Department of Public Utilities

19 Why produce toxins? -when toxin is present, filtration rate of wedge clams drops from 28%/d to 10%/d. Rangia cuneata

20 Cyanotoxin Effects on Ecosystem Services Top: effects of exposure to dissolved Microcystin on clearance rates of Rangia. Clearance rate (L g DW -1 h -1 ) R² = 0.94 CR 50 = 0.40 µg L Microcystin (µg L -1 ) Bottom: likelihood of exceeding Microcystin concentrations at various levels of CHLa. Probability of exceedence 100% 75% 50% 25% N Obs > 0.4 µg L-1 > 0.8 > 1.6 > Observations 0% CHLa (µg L -1 ) 0

21 Nutrient Inputs to Tidal-fresh James Annual inputs of nitrogen and phosphorus to the tidal fresh segment of the James.