Geologic sources of nutrients for aquatic ecosystems (Invited)
Abstract
Nutrient inputs from geologic materials are not typically considered an ecologically significant source of nutrients for freshwater aquatic ecosystems. However, in volcanic terrains where regional groundwater interacts with volcanic and underlying sedimentary deposits, nutrients (nitrogen and phosphorus) from geologic sources can provide ecologically significant inputs of nutrients to fuel aquatic food webs. The Big Springs-Shasta River complex emanating from the flanks of Mt. Shasta, a stratovolcano in northern California, creates a unique ecological niche that we propose as the explanation for the exceptionally high historical abundances and productivity of salmonids in the Shasta River. The Big Springs complex is a slightly-thermal springs (natural flow of 2.6 m3/s) that is the primary source of water for the Shasta River. The spring waters have a mean recharge elevation of 2880 m on Mt. Shasta. During the 20-50 years of transport as groundwater, both nitrogen and phosphorus are released from the underlying marine sedimentary and volcanic rocks. Mean NO3-N and soluble-reactive PO4-P concentrations over a two year period were 0.48 mg/L and 0.15 mg/L, respectively. The PO4 concentrations are in equilibrium with hydroxyapatite (Ca2OHPO4) suggesting that release of PO4 by chemical weathering of the highly weatherable volcanic deposits is the primary source of the PO4. The primary source of nitrogen is from detrital organic matter incorporated in the marine sedimentary rocks during diagensis. This “geologic” nitrogen is released from rocks by hydrothermal waters and transported with the groundwater. The nitrogen and phosphorus coupled with year round consistent water flow volumes and thermal buffering (10-12o C) fuel primary productivity and enhance food web productivity. Abundant nutrients allow for high rates of primary productivity, providing food for invertebrates, which ultimately comprise the primary food source for salmonids. These volcanic-derived, spring-fed habitats represent exceptional sites for salmonid habitat conservation and restoration activities. The potential for similar volcanic-groundwater conditions along the northern circum-Pacific Ring of Fire provide global significance to these findings. The hydrology of these spring-fed systems is expected to be sensitive to global climate change, which may result in adverse impacts on salmonid fisheries and restoration activities.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H52D..03D
- Keywords:
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- 0470 BIOGEOSCIENCES / Nutrients and nutrient cycling;
- 1813 HYDROLOGY / Eco-hydrology;
- 1830 HYDROLOGY / Groundwater/surface water interaction;
- 1871 HYDROLOGY / Surface water quality