State of the Lake 2009 - Tahoe Environmental Research Center ...

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ASIAN CLAM Increased Algae Along the southeastern portions of Lake Tahoe during July through September 2008 dense algal blooms of the green filamentous algae Zygnema and Spirogyra were often co-located The 2008 algal bloom reached estimated densities of approximately 125 mg Chl/m2, which is considered to be at or above nuisance levels. The primary bloom extended as significant patches from South Zephyr Point to Elk Point. Additional patches of bright green algae were observed from Zephyr Cove to Timber Cove along the south shore. TAHOE: STATE OF THE LAKE REPORT 2009 with Asian clam beds. These are both filamentous green algal species, which may exist attached or unattached to substrate, whose accelerated growth in other lakes and reservoirs has been Excretion of nutrients by clams is a natural part of their feeding and growth. Nitrogen and phosphorus contained in the clam excretion readily stimulates algal growth. This is one of the most likely sources of nutrients fueling the observed algal growth. Other contributing factors could include smoke and ash associated with wildfires, warming in the nearshore zone, and urban runoff. However, the fact that this bloom of bottom algae persisted for so long supports the idea that clam excretion played an important role. linked to increased levels of nutrient in the water column, sometimes as a result of bivalve excretion. An extended algal bloom has long lasting impacts on the nearshore condition of Lake Tahoe. Residual dead and dying biomass is washed up onto south shore beaches where it decomposes and influences nearshore water quality. TERC.UCDAVIS.EDU 6.4
ASIAN CLAM Asian Clam Excretion Experiment Researchers conducted simple experiments to observe the rates of nitrogen and phosphorus excretion by Asian clams. For a 12-hour period, five similarly sized clams were placed in a single beaker containing 250 mL of filtered lake water and incubated at both 19 °C (Lake Tahoe nearshore summer water temperature) and 4 °C TAHOE: STATE OF THE LAKE REPORT 2009 (Lake Tahoe nearshore winter water temperature). Results from the warm temperature (19 °C) experiment show that larger clams excrete more N and P than smaller clams and both excrete more than background concentrations in Lake Tahoe water column. The largest clams in this experiment were approximately 25 mm and excrete at rates an order of magnitude larger than the smallest clam size class considered here. Furthermore, tests designed to evaluate the impact of clam excretion products on algal growth showed a dramatic (3-fold) increase in phytoplankton biomass over a 7-day incubation period in the laboratory. TERC.UCDAVIS.EDU 6.5
Page 1 and 2: TAHOE: STATE OF THE LAKE REPORT 200
Page 3 and 4: INTRODUCTION The University of Cali
Page 5 and 6: EXECUTIVE SUMMARY (CONTINUED FROM P
Page 7 and 8: ABOUT LAKE TAHOE AND THE TAHOE BASI
Page 9 and 10: MAP OF TAHOE BASIN DATA COLLECTION
Page 11 and 12: Rainbow, Brook, Brown and Lake trou
Page 13: 100% 90% 80% 70% 60% 50% 40% 30% 20
Page 17 and 18: ASIAN CLAM Asian Clam Size Distribu
Page 19 and 20: Temperature ( o F) 60 55 50 35 30 M
Page 21 and 22: Temperature ( o F) 70 60 50 40 30 2
Page 23 and 24: Inches 70 60 50 40 30 20 10 0 METEO
Page 25 and 26: Percent 80 70 60 50 40 30 20 10 0 M
Page 27 and 28: PHYSICAL PROPERTIES TERC.UCDAVIS.ED
Page 29 and 30: Feet 6232 6230 6228 6226 6224 6222
Page 31 and 32: Temperature ( o F) TERC.UCDAVIS.EDU
Page 33 and 34: Temperature ( o F) TERC.UCDAVIS.EDU
Page 35 and 36: Density Difference (kilograms per c
Page 37 and 38: Mean daily streamflow (cubic feet p
Page 39 and 40: NUTRIENTS AND PARTICLES TERC.UCDAVI
Page 41 and 42: TERC.UCDAVIS.EDU NUTRIENTS AND PART
Page 43 and 44: Metric Tons TERC.UCDAVIS.EDU 10 8 6
Page 45 and 46: Dissolved inorganic nitrogen (micro
Page 47 and 48: Nitrate−nitrogen (micrograms per
Page 49 and 50: BIOLOGY 10
Page 51 and 52: BIOLOGY Algae abundance Yearly sinc
Page 53 and 54: BIOLOGY Depth of chlorophyll maximu
Page 55 and 56: BIOLOGY TAHOE: STATE OF THE LAKE RE
Page 57 and 58: BIOLOGY Nutrient limitation of alga
Page 59 and 60: BIOLOGY Shoreline algae distributio
Page 61 and 62: TERC.UCDAVIS.EDU CLARITY Annual ave
Page 63 and 64: Depth (feet) TERC.UCDAVIS.EDU CLARI
Page 65:
TERC.UCDAVIS.EDU OUTREACH AND EDUCA
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State of the Lake 2009 - Tahoe Environmental Research Center ...

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