2022 Nutrient Source Identification in Groundwater and Periphyton Along the Nearshore of Lake Tahoe

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Finding Details

High concentrations of phosphorus (P) and nitrogen (N) are responsible for excessive, or nuisance algal blooms in many ecosystems world-wide, and climate change is predicted to exacerbate the problem1,2. Excessive nutrients supplied to the nearshore zone of Lake Tahoe may have significant consequences to ecological communities, water clarity, and water quality. The nearshore zone represents the interface between the surrounding watershed and into the lake to about a depth of 30 meters3. Recent changes in periphyton biomass in this zone may indicate changes in nutrient supply from human sources. Therefore, management actions that serve to limit external contributions of nutrients to the watershed will become even more important to Lake Tahoe in the future.

Question 1: What are the sources of N and P in groundwater?

Elevated concentrations of N and P in groundwater will be related to anthropogenic enrichment from fertilizer and effluent; however, seasonal variations in hydrological processes may contribute natural sources to groundwater and periphyton at various times. Nutrient transport to the nearshore environment is dependent on physical drivers within the watershed that are temporally and spatially variable. Studies have shown that N and P concentrations in Lake Tahoe streams are typically greatest during first flush events where runoff from the landscape, channel, and urban areas contribute to increased nutrient concentrations in the lake. Precipitation and recharge within the landscape mobilize natural N and P from forest soils, leaf litter and alders. Nutrient inputs from recharge also increase concentrations in groundwater and stimulate periphyton growth along the nearshore. Thus, characterizing the relative contributions of nutrient sources to streams and groundwater during the first flush and later stages of snow-melt periods can be used by water resource managers to mitigate anthropogenic influences to nutrient enrichment.

Question 2: What are these sources identifiable in nearshore periphyton?

Sources identified in groundwater and periphyton will be similar where groundwater plays a role in the transport of nutrients to the nearshore. However, groundwater may not be important at every periphyton hot spot along the shore of Lake Tahoe. This study is an important first step in gathering multi-isotopic nutrient source information from both periphyton biomass and groundwater.

The peer-reviewed article will be posted here once published.