Patterns and filters of eutrophication endpoints in Elkhorn Slough

Transcription

1 Patterns and filters of eutrophication endpoints in Elkhorn Slough Brent Hughes, Kerstin Wasson, John Haskins Elkhorn Slough National Estuarine Research Reserve

2 What is Eutrophication? Source: Associated Press

3 Conceptual Evolution of Coastal Eutrophication Early models focused on lakes, which have a direct response to nutrient addition (Volenweider 1976) Direct Responses Nutrients Primary Productivity Organic Deposition Microbial Activity Hypoxia From Cloern (2001)

4 Conceptual Evolution of Coastal Eutrophication Current models recognize variability in response among estuaries due to various filters, as well as indirect responses. Nutrients Filters Turbidity Depth Currents Tides Marsh Direct Responses Primary Productivity Organic Deposition Microbial Activity From Cloern (2001) Indirect Responses Bottom DO Community Diversity Food Webs

5 Study Goals 1. Characterize the spatial dynamics of eutrophication in Elkhorn Slough 2. Understand filters of eutrophication, with an emphasis on tidal range. 3. Focus on eutrophication within an estuary, instead of between estuaries.

6 Elkhorn Slough, CA: a highly altered estuary

7 Eutrophication Filter: Tidal Range

8 Background information Elkhorn Slough has high nutrient concentrations and loading (54.4kg NO 3 /acre/y) (Johnson 2008). Elkhorn Slough has high primary productivity indicating hypereutrophication (860 g/c/m 2 /y) Tidally restricted areas have decreased benthic diversity and abundance (Oliver et al. 2009).

9 Macroalgae: highly abundant at most sites Ulva often nutrient limited, enhanced by agricultural inputs; Algal mats can affect dissolved oxygen and benthic communities

10 Macroalgal Abundance: related to tidal exchange

11 Water Column Chlorophyll a: high at all sites Affects dissolved oxygen and light availability in the water column

12 Chl a indicates eutrophic conditions Concentrations not significantly different in full vs. muted sites Eutrophic lines based on Bricker et al. (2003) High Eutrophication Moderate Eutrophication

13 Sediment Anoxia: Affects benthic invertebrate communities and feeding by other animals.

14 Sediment Anoxia: related to tidal exchange A much narrower layer at the top of the mud is well oxygenated at muted vs. full tidal sites

15 Hypoxia Events: More frequent in tidally restricted areas.

16 Nutrients do not explain eutrophic patterns (Nitrate/Phosphate)

17 Nutrients do not explain eutrophic patterns (Nitrate/Phosphate)

18 Eutrophication End Points

19 Eutrophication End Points: Explained by Tidal Exchange

20 Hypoxia Filter: Maximum Tidal Range

21 Summary Elkhorn Slough is a highly eutrophic estuary, yet varies within the estuary as moderate to hyper eutrophic. Sites with a decreased tidal range have lower intertidal algal cover, but more floating algal mats, and higher phytoplankton concentrations. Sites with a decreased tidal range have a higher frequency of hypoxia events, and more anoxic sediments.

22 Conclusions Tidal range is a strong predictor of degree of eutrophication between sites within the estuary, and thus serves as an important "filter" for expression of eutrophication Artificial tidal restriction can result in expression of severe eutrophication in highly nutrient loaded estuaries Even a moderate increase in tidal range behind water control structures can lead to substantial improvements in water quality

23 Acknowledgements Funding Sources: NERR Water Quality Program Community Foundation for Monterey County/PG&E Non-Point Source Pollution Grant (Grant # ) Elkhorn Slough Foundation Monterey County Water Resources Agency Field Assistants: Sue Shaw, Ron Eby, Joseph Hatfield, Rikke Kvist Preisler, Patty Brown Lab Analysis: Sara Tanner (MLML), Moss Landing Marine Lab Chemical Oceanography Lab, Nick Welschmeyer (MLML), Theresa Hodges (Monterey County Consolidated Chemistry Lab) Other Data Sources: Monterey Bay Aquarium Research Institute/ Land Ocean Biogeochemical Observatory (Ken Johnson), A. Gee