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Geology topics

Jonathan Behrens

Publications and source records attributed to Jonathan Behrens.

2 recordsLinked to original sources

Practical pathways for protecting headwater streams in urbanizing areas

Headwater streams are diverse ecosystems and important sources of water and dissolved and particulate resources to the downstream river network. However, across the world, they are rapidly being degraded or lost through human activities, particularly urban development. This degradation and loss have negative consequences for the structure and function of headwater streams, as well as downstream river networks. Despite long-held recognition of the ecological value of headwater streams and the impacts of their widespread loss, there remains a large gap between developing strategies and tangible action. To address this gap, we, a group of cross-disciplinary researchers and practitioners from multiple organizations and locations, developed a framework to guide strategic decision-making and a comprehensive set of structural and nonstructural tools that can be used to protect headwater streams in urbanizing areas where opportunities to protect waterway health are being considered by local waterway practitioners and the community. The framework was tested by applying it to 4 contrasting case studies of urbanization with different physiographic, policy, and legislative settings. Our evaluation showed that the framework provides a useful generic mechanism that can be used by policymakers, planners, and other stakeholders to diagnose the status of headwater stream protection in a variety of urban areas and to support structured stakeholder conversations about what is desirable, practical, and achievable for their context.

Freshwater Science

Diverging fish biodiversity trends in cold and warm rivers and streams

Worldwide, freshwater systems contain more than 18,000 fish species 1,2,3 , which are critical to the functioning of these ecosystems 4 and are vital cultural and economic resources to humans 5,6,7 ; despite this value, fish biodiversity is at risk globally 8,9 . In the USA, leading threats to fish communities in rivers and streams include climate change and invasive fish introductions and game fish stocking by humans 10,11,12,13,14 . Here we harmonized US federal biomonitoring datasets with 389 species spanning 27 years (1993–2019) and 2,992 sites to analyse trends in fish biodiversity. In cold streams (past summer stream temperatures below 15.4 °C), fish abundance and richness declined by 53.4% and 32% over 27 years, respectively, and uniqueness increased. Periodic (large-bodied, late-maturing) fishes increased, and opportunists (small-bodied, short generation time, ‘r-selected’) decreased, possibly due to proliferation of native or introduced game fishes. In warm streams (stream temperatures greater than 23.8 °C), fish abundance and richness increased by 70.5% and 15.6% over 27 years, respectively, and communities homogenized. Small opportunistic fishes replaced large periodic fishes. Intermediate streams (stream temperatures 15.4–23.8 °C), representing the average stream, had minimal changes in fish biodiversity through time. Interactions between warming and introduced fish were associated with increased rates of degradation to local fish biodiversity. Given the magnitude of these changes in a relatively short time span, there is an urgent need to curb degradation of fish biodiversity caused by fish introductions and warming water temperatures.

continental United States