Species-Richness Responses to Water-Withdrawal Scenarios and Minimum Flow Levels: Evaluating Presumptive Standards in the Tennessee and Cumberland River Basins

Abstract

Water-resource managers are challenged to balance growing water demand with protecting aquatic ecosystems and biodiversity. Management decisions can benefit from improved understanding of water-withdrawal impacts on hydrologic regimes and ecological assemblages. This study used ecological limit functions for fish groups within the Tennessee and Cumberland River basins to predict species richness responses under simulated constant-rate (CR) and percent-of-flow (POF) withdrawals and for different minimum flow level protections. Streamflow characteristics (SFC) and richness were generally less sensitive to POF withdrawals than CR withdrawals among sites, fish groups, and ecoregions. Species richness generally declined with increasing withdrawals, but responses were variable depending on site-specific departures of SFCs from reference conditions, drainage area, fish group, ecoregion, and minimum flow level. Under POF withdrawals, 10% and 20% daily flow reductions often resulted in loss of <1 species and/or ≤5% richness among fish groups. Median ecological withdrawal thresholds ranged from 3.5–31% for POF withdrawals and from 0.01–0.92 m3/s for CR withdrawals across fish groups and ecoregions. Application of minimum flow level cutoffs often resulted in damping effects on SFC and richness responses, indicating that protection of low streamflows may mitigate hydrologic alteration and fish species richness loss related to water withdrawals. Site-specific and regionally summarized responses of flow regimes and fish assemblages under alternative withdrawal strategies in this study may be useful in informing water-management decisions regarding streamflow allocation and maintaining ecological flows.

New Integrated Hydrologic Approach for the Assessment of Rivers Environmental Flows Into the Urmia Lake

“…According to Figure 10, the flow allocated to the Urmia Lake in these six years is much higher than the volume calculated through the GEFC-Class C method, but by the 1361Mm 3 allocation of water to the Urmia Lake only 44% of EWR of the lake has been supplied. However, if the EWR of the Urmia Lake be considered by Equation 8, the water volume equal to or more 473 than 70.5% of the natural flow of the river as e-flow should be allocated to the lake.…”

“…Figure 10, shows that in all six years, the GEFC method in EMC-C has the lowest volume of allocated water concerning the EWR of the lake (3084Mm 3 ) and on average 26% of the annual volume of natural river flow equivalent to 670Mm 3 of water is delivered to the lake each year. Also, the average volume of water allocated to the Urmia Lake in the EFR-Ann method class-ADJ with 71% and the EFR-Mon method class-ADJ with 74% of the natural flow of the river will be equivalent to 1852Mm 3 and 1938Mm 3 , respectively. In the period from 2010 to 2015, the average natural flow volume of rivers was equal to 2618 Mm 3 , equivalent to 60% of the long-term average natural flow volume of these rivers.…”

“…However, if the EWR of the Urmia Lake be considered by Equation 8, the water volume equal to or more 473 than 70.5% of the natural flow of the river as e-flow should be allocated to the lake. So, the volume 474 of water that can be allocated to the Urmia Lake must be more than 1844Mm 3 which is equal to 60% of the lake EWR, that both EFR-ADJ-Ann and EFR-ADJ-Mon methods can supply this amount of water.…”

New integrated hydrologic approach for the assessment of rivers environmental flows into the Urmia Lake

“…Nowadays, intense competition between ecosystem and water resource development projects, especially in rivers has emerged with the increasing population and the human need for water 1 . Many aquatic ecosystems are declining and disappearing due to human interventions in the overuse of water resources 2 , 3 and climate change 4 – 6 . Environmental flow (e-flow) allocation is an important factor in maintaining ecosystems, along with flora and fauna species 7 .…”

Special Issue: Environmental Flows, Ecological Quality, and Ecosystem Services

“…The main group of papers focuses on the conceptual, quantitative, and qualitative links of flow regime and e-flows with river ecosystem functions and values, such as the preservation and ecological status of inland wetlands [1], the functions and values of temporarily closed estuaries [2], the preservation of fish species richness [3], the impact on fish spawning period [4], the ecological quality, bird diversity and shellfish fisheries in a lowland river and its coastal area [5], and the ecosystem productivity of coastal areas [6]. Moreover, one of the papers [7] performs an in-depth review of ecohydrological links in the lower Ebro River and its Delta, which is one of the most studied cases regarding the impacts of flow regime alteration on socioecological functions and values.…”