Protecting streams from rural land conversion: Do strong regulations work?

Background/Question/Methods Our goal is to answer a fundamental yet controversial question: “Do strong land use regulations protect aquatic critical areas and biological resources?” This question has broad relevance. Public institutions throughout the U.S. face the challenge of integrating population growth, land conversion, and environmental protection. Counties play a central role by regulating zoning, clearing, grading, and storm water management, which are key mechanisms of change. King County, the population center of Puget Sound (Washington State), illustrates this challenge. King County strengthened land use regulations in 2005 to reflect the best available science. Strong regulations produced great controversy. This created an opportunity to examine whether rural development can coexist with healthy aquatic ecosystems. We used this opportunity to begin a longitudinal study of regulatory effectiveness in six treatment and three control catchments. We sought to understand how streams respond to rural land use change under particular regulations over time and space. We desired a better understanding of cause-and-effect relationships to identify specific problems and solutions. We reconstructed historical changes from archival records to test for legacy effects and compare trajectories. We are presently tracking four main indicators: hydrology, benthos, water quality, and channel complexity. Our methods include stream gaging, invertebrate sampling, sonde deployments, stream surveys, and chloride tracer experiments. We are quantifying landscape transitions at fine scales from orthophotos and evaluating permit compliance. We linking ongoing development with streams in a spatially-explicit framework to quantify potential cumulative impacts. We will synthesize our findings with Bayesian belief networks that estimate our certainty in regulatory effectiveness, considering the observed level of development, permit complicance, and the strength and concordance of observed responses in indicators.

Results/Conclusions This study is ongoing though preliminary results are available. Stream benthos demonstrate resiliency; all streams range from good to excellent condition despite being logged 60-100 years ago. Chloride experiments established rating curves for comparing stream complexity across discharges and years, with exceptional precision. Streamflow patterns varied substantially among physically-matched catchments with similar land use. Present-day land cover analysis is ongoing. Reconstructions indicate catchments are on similar trajectories, though land use changes are autocorrelated, confounding the attribution of current conditions to past impacts. Next steps in this ongoing study are to better isolate land use-related changes by accounting for variability attributable to physical differences between catchments and regional climate patterns.