Abstract
Managed aquifer recharge (MAR) is typically used to enhance the agricultural water supply but may also be promising to maintain summer streamflows and temperatures for cold-water fish. An existing aquifer model, water temperature data, and analysis of water administration were used to assess potential benefits of MAR to cold-water fisheries in Idaho’s Snake River. This highly-regulated river supports irrigated agriculture worth US $10 billion and recreational trout fisheries worth $100 million. The assessment focused on the Henry’s Fork Snake River, which receives groundwater from recharge incidental to irrigation and from MAR operations 8 km from the river, addressing (1) the quantity and timing of MAR-produced streamflow response, (2) the mechanism through which MAR increases streamflow, (3) whether groundwater inputs decrease the local stream temperature, and (4) the legal and administrative hurdles to using MAR for cold-water fisheries conservation in Idaho. The model estimated a long-term 4%–7% increase in summertime streamflow from annual MAR similar to that conducted in 2019. Water temperature observations confirmed that recharge increased streamflow via aquifer discharge rather than reduction in river losses to the aquifer. In addition, groundwater seeps created summer thermal refugia. Measured summer stream temperature at seeps was within the optimal temperature range for brown trout, averaging 14.4 °C, whereas ambient stream temperature exceeded 19 °C, the stress threshold for brown trout. Implementing MAR for fisheries conservation is challenged by administrative water rules and regulations. Well-developed and trusted water rights and water-transaction systems in Idaho and other western states enable MAR. However, in Idaho, conservation groups are unable to engage directly in water transactions, hampering MAR for fisheries protection.
Highlights
In the Western USA, important aquatic ecosystems and recreational fisheries often occur in river basins with large irrigated agricultural diversions, resulting in conflicts between water for irrigation and environmental streamflow needs [1,2,3]
This study aims to understand the potential for managed aquifer recharge (MAR) to benefit cold-water ecosystems while maintaining irrigated agriculture in Idaho’s Henry’s Fork Snake River
The steady-state simulation using ESPAM2.1 predicted that 37% of the water volume delivered to the Egin Lakes MAR site will increase streamflow in the modeled reach of the Henry’s Fork over the long term, and the balance will benefit other river reaches in the basin (Figure 3)
Summary
In the Western USA, important aquatic ecosystems and recreational fisheries often occur in river basins with large irrigated agricultural diversions, resulting in conflicts between water for irrigation and environmental streamflow needs [1,2,3]. Climate change exacerbates these conflicts, as precipitation regimes shift from snowfall to rainfall and evaporative demand increases, leading to flashier streamflow in winter and spring and reduced baseflow through summer and fall [4,5]. The potential of MAR to benefit cold-water ecosystems while maintaining irrigated agriculture requires (1) understanding the physical hydrology between the recharge site and the stream, (2) estimating temperature differences at groundwater seeps in the river and ambient temperatures, and (3) understanding administrative water rules to apply MAR to benefit cold-water habitat
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