Abstract
There have been significant increases in stream flow in many rivers of the Upper Midwestern United States since 1980. Increased summer flows may negatively impact ecological processes, including aquatic organisms’ life cycles. The smooth softshell (Apalone mutica) and wood turtle (Glyptemys insculpta) are threatened by alteration of stream flow regime and other changes to river ecosystems in the Upper Midwest. We hypothesized that prolonged duration of high summer flows would reduce time available for nesting. We assessed hydrologic change using the Indicators of Hydrologic Alteration program and stream gauge data, characterized physical properties of sandbars, surveyed turtle nesting sites and assessed historical channel change using aerial photos in GIS on five Upper Midwest rivers. A river stage-sandbar area relationship was developed to determine the effect of prolonged summer flow duration on turtle nesting opportunity for the 1940–2009 time period. Suitable water levels have declined since 1980 in the agricultural watersheds of southern Minnesota likely delaying hatching and reducing survival, particularly for aquatic turtles such as A. mutica. In contrast to the agricultural watersheds, there was no significant change in the northern forested rivers’ stream flow and sandbar availability during the nesting season. Management to reduce summer stream flow in agricultural watersheds and protection of known nest sites could benefit threatened aquatic turtle populations.
Highlights
Hydrologic regime is an important regulator of ecological processes in rivers [1]
We examined an earlier period of stream flow record (1900–1940 for streams where data was available) to identify the earliest possible dates available for turtle nesting on each river based on the timing of sandbar emergence
Column 4 lists the change in the coefficient of variation (C.V.), a measure of stream flow variability of the daily average flows over a year
Summary
The hydrologic response of rivers to change may include alteration of stream flow magnitude, duration, timing, frequency and variability all of which can alter a river’s geomorphologic and riparian characteristics in various ways with consequences for stream biota [2]. Hydrologic and geomorphic change can affect aquatic biota in numerous ways since their life cycles are often tied to the variability of water level in rivers. Aquatic organisms are at risk to hydrologic change since there are a large number of threatened or endangered aquatic species in rivers, including fish, mussels, and riverine turtles [5]. Some studies have been done quantifying eco-hydrological interactions mostly focusing on how flow magnitude change impacts fish or invertebrate species [3]. Very few studies exist that relate changes in the duration and timing of stream flow change to the life cycles of riverine amphibians or reptiles
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