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Los Angeles Regional Water Quality Control Board, November 4, 2004 1 Total Maximum Daily Load for Nutrients in Malibu Creek and Lagoon Melinda Becker and.

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Presentation on theme: "Los Angeles Regional Water Quality Control Board, November 4, 2004 1 Total Maximum Daily Load for Nutrients in Malibu Creek and Lagoon Melinda Becker and."— Presentation transcript:

1 Los Angeles Regional Water Quality Control Board, November 4, Total Maximum Daily Load for Nutrients in Malibu Creek and Lagoon Melinda Becker and Rod Collins Los Angeles Regional Water Quality Control Board November 4, 2004

2 Los Angeles Regional Water Quality Control Board, November 4, Nutrient Impairments n Aquatic toxicity, generally related to nitrogen as ammonia n Excessive growth of algae and vascular plants caused by elevated levels of nitrogen and or phosphorus – leads to low dissolved oxygen – Impairment of aquatic habitat – Impairment of recreational use

3 Los Angeles Regional Water Quality Control Board, November 4, Malibu Creek Nutrient TMDLs n EPA established Malibu Creek and Lagoon Nutrients TMDL on March 22, n EPA found that the evidence of algal impairment was less conclusive for winter time than during summer conditions. n EPA established different numeric targets for winter and summer.

4 Los Angeles Regional Water Quality Control Board, November 4, USEPA TMDL Numeric Target n Nitrogen and Phosphorus

5 Los Angeles Regional Water Quality Control Board, November 4, Draft Regional Board TMDL n Staff’s focus has been to increase the understanding of the impact of nutrients on excessive growth of algae and vascular plants and to refine the TMDL and allocations accordingly. n Identified unanswered questions in EPA TMDL and contracted special studies.

6 Los Angeles Regional Water Quality Control Board, November 4, Unanswered Questions n Is the Creek impaired due to excessive algal growth in the winter? n What are the controlling or limiting factors for algal growth? n Do wintertime discharges contribute to summertime impairments in the Lagoon? n Does contaminated groundwater impact surface water nitrogen levels?

7 Los Angeles Regional Water Quality Control Board, November 4, Recent Studies n Survey of algal biomass and limiting factors (SCCWRP /UC Santa Barbara) n Bioassessment in coastal watersheds (UCLA) n Impact of wet weather discharges on summer impairment in the Lagoon (SCCWRP) n OWTS Risk Assessment (City of Malibu) n Groundwater Evaluation under the Rancho Las Virgenes Farm (Las Virgenes Municipal Water District, report pending)

8 Los Angeles Regional Water Quality Control Board, November 4, Importance of Benthic Algae n Prior surveys focused on floating algal mats n New surveys employed more quantitative methods and included both floating and benthic algae (diatoms)

9 Los Angeles Regional Water Quality Control Board, November 4, Wintertime Impairment? n Wintertime impairment –Recent surveys that quantify benthic algae (diatoms) show wintertime impairment –Impairment for floating algae based on > than 30 % cover (Biggs) –Impairment for benthic algae (diatoms) based on>60% cover (Biggs)

10 Los Angeles Regional Water Quality Control Board, November 4, Factors that Stimulate Growth n Nutrients: nitrogen and phosphorus n Light n Current n Others: grazing, substrate, temperature, etc.

11 Los Angeles Regional Water Quality Control Board, November 4, Nutrients n Nitrogen (N) and/or phosphorus (P) may limit growth n N to P ratios predict limiting nutrient –Ratios of < 10 N to 1 P, suggest Nitrogen limitation –Rations > 30 N to 1 P, suggest Phosphorus limitation –Between 10 and 30, co-limiting n High levels saturate growth, neither limiting without drastic reductions

12 Los Angeles Regional Water Quality Control Board, November 4, Light as a Controlling Factor n Recent studies show that light merely determines the type of algae present and does not impact total algal biomass n Light promotes floating algae, but in shaded areas benthic algae (diatoms) flourishes if sufficient nutrients are available

13 Los Angeles Regional Water Quality Control Board, November 4, Current as a Controlling Factor n Common wisdom suggested that high currents sweep algae away. Therefore, algae not a problem during wet weather. n More true for floating algae, less true for benthic algae n Benthic algae recovers quickly after a storm event n Faster currents deliver more nutrients to benthic algae

14 Los Angeles Regional Water Quality Control Board, November 4, SCCWRP/UCSB Study n In many areas nutrient levels were saturated, thus drastic reductions would be required to limit algal growth. n However, data suggest that the site below Tapia WRF is nitrogen limited during the discharge prohibition period. n In general, reducing nutrient concentrations would probably reduce benthic diatoms but have less impact on floating macroalgae.

15 Los Angeles Regional Water Quality Control Board, November 4, UCLA Study: General Trends In shaded areas bottom algae is more abundant versus unshaded areas, and positively correlated with phosphorus. In unshaded areas floating algae is more abundant versus shaded areas and positively correlated with nitrogen. In shaded areas high nutrients are correlated to poor conditions of aquatic invertebrate communities.

16 Los Angeles Regional Water Quality Control Board, November 4, Malibu Lagoon Study n Dense stands of Ruppia maritima results in low DO during dry season in western Lagoon. n Nutrient levels in surficial sediment of western portion of Lagoon are greater than some of the most eutrophic systems studied worldwide.

17 Los Angeles Regional Water Quality Control Board, November 4, Update – LARWQCB TMDL n Slide of lagoon

18 Los Angeles Regional Water Quality Control Board, November 4, Malibu Lagoon Study n Wet-weather discharges of particulate TN and TP from Malibu Creek settle in the western Lagoon n N and P from sediment is strongly linked to excessive growth of R. maritima and low DO in the Lagoon during summer. n Releases from sediment in the summer represents 18% of TN and 5% TP total dry- weather loading to the Lagoon.

19 Los Angeles Regional Water Quality Control Board, November 4, Malibu Lagoon Study n Deposition of particulate organic N and P major source to sediment n Diffusion of high dissolved inorganic nitrate/nitrite from surface water to sediment only about 5% of loading to Lagoon sediment n Deposition occurs during episodic rain events n Nutrient sources may result from stormwater runoff or instream sediment, instream algae or ocean sediment or ocean algae.

20 Los Angeles Regional Water Quality Control Board, November 4, Staff’s Conclusion n Based on the weight of evidence, Staff concludes: –The Creek is impaired for algae during the winter wet-weather season –Wintertime nutrient discharges to the Creek and Lagoon contribute to summertime impairments in the in the western Malibu Lagoon –Reducing nitrogen and phosphorus will reduce eutrophication

21 Los Angeles Regional Water Quality Control Board, November 4, Staff Recommendation n Extend EPA’s recommended summer time numeric targets of 1.0 mg/L total nitrogen and 0.1 mg/L total phosphorus to the winter season.

22 Los Angeles Regional Water Quality Control Board, November 4,

23 Los Angeles Regional Water Quality Control Board, November 4, Background - Impairments n Map with nutrient concentrations

24 Los Angeles Regional Water Quality Control Board, November 4, Nutrient Sources n Tapia WRF n Malibu OWTS and associated contaminated groundwater n Rancho Las Virgenes, historic sludge injection and associated contaminated groundwater n Other OWTSs and potential contaminated groundwater n Runoff from golf courses and other landscaped areas n Runoff from livestock holding areas

25 Los Angeles Regional Water Quality Control Board, November 4, Issues Issues n Potential Impacts of Recommended Actions on Tapia WRF –Reduced nitrogen and phosphorus load allocation n 14.6 mg/L TN to 1.0 mg/L n 2.6 mg/L TP to 0.1 mg/L –Investigate alternatives to Malibu Creek discharge, such as: n Increased discharge at LA River outfall n Ocean outfall

26 Los Angeles Regional Water Quality Control Board, November 4, Update – LARWQCB TMDL n Map of nitrogen contributing areas

27 Los Angeles Regional Water Quality Control Board, November 4, Update – LARWQCB TMDL n Map of sludge injection areas

28 Los Angeles Regional Water Quality Control Board, November 4, Board Direction n Staff is seeking comments and direction from the Board on: –General findings and conclusions –Additional studies –Implementation time frames –Other

29 Los Angeles Regional Water Quality Control Board, November 4, Questions n Staff contacts: –Rod Collins (213) –Melinda Becker (213)


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