Redwood Shores Lagoon August Monthly Water Quality Monitoring Report

Transcription

1 Redwood Shores Lagoon August Monthly Water Quality Monitoring Report Prepared for Redwood City Public Works Services Department 1400 Broadway Redwood City, CA Prepared by Clean Lakes, Inc. P. O. Box 3186 Martinez, CA Page 1 of 6

2 City of Redwood City staff Richard Chaffey performed the August monthly monitoring on August 13, In R-1 thru R-5 general water quality measurements of dissolved oxygen, clarity (as turbidity), salinity, ph, and temperature were recorded. Nutrients, nitrate as N and dissolved ortho-phosphate as P were also sampled for in R-1 thru R-5. During each sampling, observations were recorded regarding floatables, oil/grease films and scum, water discoloration, algae and aquatic plant growth, and any presence of dead birds or fish. NUTRIENTS There were no positive readings for Nitrate as N in the lagoon again however there were positive readings in all of the lagoons for Orthophosphate as P. The highest reading of 0.60 mg/l was in R-1 which is I believe the highest reading to date and well above the reading in July. The rest of the counts were also much higher than average with all of them being higher than ever recorded since CLI started sampling. With the level this high the City and Waterworks (the maintenance contractor) should keep a close eye on the lagoon for potential algae blooms. CLI will talk to Waterworks to see if there was any event that occurred on the lagoons that could help explain the increased levels. Both phosphorus and nitrogen are essential nutrients for the plants and animals that make up the aquatic food web. Since phosphorus is the nutrient in short supply in most fresh waters, even a modest increase in phosphorus can, under the right conditions, set off a whole chain of undesirable events in a stream including accelerated plant growth, algae blooms, low dissolved oxygen, and the death of certain fish, invertebrates, and other aquatic animals. There are many sources of phosphorus, both natural and human. These include soil and rocks, wastewater treatment plants, runoff from fertilized lawns and cropland, failing septic systems, runoff from animal manure storage areas, disturbed land areas, drained wetlands, water treatment, and commercial cleaning preparations. Page 2 of 6

3 Inorganic nitrate as N should be less than 0.3 mg/l to avoid algal blooms Excessive concentrations of nitrate in lakes and streams greater than about 5 milligrams per liter (measured as nitrogen), depending on the water body, can cause excessive growth of algae and other plants, leading to accelerated eutrophication or "aging" of lakes, and occasional loss of dissolved oxygen. Animals and humans cannot use inorganic forms of nitrogen, so nitrate is not a nutrient for us. Since phosphorus is often scarce in freshwater ecosystems, it's typically a limiting nutrient, meaning that it limits the amount of life the system can sustain. When humans add phosphate-rich sewage or agricultural runoff, algae growth may no longer be limited by the scarcity of phosphorus in its environment and may grow out of control. In order to control algae growth, the EPA recommends that phosphate levels not exceed.05 milligrams per liter for streams discharging into lakes or reservoirs,.1 milligrams per liter for lakes and reservoirs, and.1 milligrams per liter for other streams and rivers. FECAL COLIFORM - The fecal coliform samples for R-1and R-2 were both very low with R-1 being 4 MPN/100 ml and R-2 having non-detectable levels (ND) GENERAL WATER QUALITY ANALYSIS The Dissolved oxygen levels went up or stayed about the same in R-1 through R-4. However there was a pretty significant drop in R-5 that went from 5.56 mg/l to 3.77 mg/l and even though this is not a large drop it is a significant one because it takes the level below 4 mg/l which as you can see in the table below can lead to moderate to severe production impairment of the fish and other Marine species. The temperature has stayed about the same throughout the lagoons with very minimal change from July to August. The ph readings all dropped a little bit but from July to August but are all still at ideal levels. Once again salinity fluctuated slightly in a few of the lagoons but all of the readings are around the average levels for the lagoon. The Turbidity went down in every lagoon except for R-1 which went up slightly. R-2 through R-5 all went down with R-3 having the most significant drop from 61.7 NTU to 31.7 NTU which is good to see. The general water quality of the lagoon is ok. It would be good to see the nutrient levels drop significantly and it would also be good to see the Dissolved Oxygen readings go up especially in R-5. II. NON-SALMONID WATERS DO mg/l A. Early life stages No production impairment 6.5 Slight production impairment 5.5 Moderate production impairment 5 Severe production impairment 4.5 Limit to avoid acute mortality 4 B. Other life stages No production impairment 6 Slight production impairment 5 Moderate production impairment 4 Severe production impairment 3.5 Limit to avoid acute mortality 3 Page 3 of 6

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5 Lab Results Page 5 of 6

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