This article originally appeared in the Spring 2010 issue of ESF's newsletter, Tidal Exchange.
Land management requires forward thinking and takes great patience. It is an incremental process with results measured in years, not weeks or months. The purpose of conserving land is not just to hold it, but to enhance the environment, expand habitat, and improve water quality. Over time, ESF has made impressive progress - hundreds of acres restored, gullies recontoured and planted with native grasses, and invasive species controlled.
While it is easy to measure success in terms of acreage of uplands acquired and restored, it can be very challenging to detect whether the objective of improved water quality has been achieved. Land trusts nationwide struggle with this challenge. Many factors unrelated to restoration also affect water quality, in particular interannual variation in rainfall. Furthermore, decreases in pollution through one restoration project may be offset by increased pollution from other lands in the watershed. Due to these complications, very few studies verify the direct positive correlation between restoration work and watershed well-being.
In a groundbreaking research study that’s garnering national attention, Elkhorn Slough researchers have statistically demonstrated that the land acquisition and restoration projects of ESF and ESNERR have directly translated into improved water quality in the watershed. The results are published in this month’s edition of the peer-reviewed scientific journal Estuaries and Coasts.
The ESNERR researchers Alison Gee, Kerstin Wasson and John Haskins employed the statistical test Before-After-Control-Impact (BACI), to tease apart differences due to restoration from those due to interannual variation in weather or other factors. To run this type of test, it is vital to have several years of data from four different data sets: prior to restoration, following restoration, sites where restoration has occurred, and sites where no restoration happened. Elkhorn Slough is one of the few areas nationwide where there is sufficient data to run the BACI test.
Data collection in the slough dates back to 1988, when scientists from Moss Landing Marine Laboratories and ESF had the foresight to initiate consistent water quality sampling at sites in two dozen wetlands of the Elkhorn Slough watershed. The program has been expanded and carried on for the past decades by the Elkhorn Slough Reserve and the Monterey County Water Resources Agency. Volunteers have collected the water samples in the field. On a shoestring budget but with the strength of partnerships between organizations and with volunteer help, these long-term monitoring data have been collected, enabling implementation
of the powerful BACI test for restoration effects.
The research study examined two major projects led by ESF, restoration of the lands draining into the Azevedo wetlands and Porter Marsh. At the Azevedo wetlands, buffers were created between the farmed lands and the wetlands with the steepest lands taken out of production. Along Carneros creek, acquisition of various key properties allowed steep eroding slopes to be restored, and land management practices to be improved in the areas that continue to be farmed. In both areas, water quality significantly improved after restoration when compared to an adjacent control site (Kirby Park) where no restoration had occurred.
The study also investigated the water quality implications of managing tide gates. Tidal exchange is restricted to the Azevedo wetlands by culverts under the railroad berm, and to Porter marsh by tide gates under Elkhorn Road. Long-term monitoring data revealed that water quality dramatically improved during periods where culverts or tidegates allowed more tidal exchange than in periods where they strongly limited tidal exchange. Indeed, the improvements due to increased tidal exchange were more dramatic than those due to land management. Changes in land management can reduce inputs of sediments, nutrients and chemicals. At the same time, habitat quality for estuarine resident fish or birds can be greatly improved locally simply by allowing for increased tidal flushing.
Study co-author Kerstin Wasson concludes, “Long-term monitoring data made possible by strong partnerships and dedicated volunteers have taught us that extensive restoration near wetlands combined with wise management of water control structures can improve water quality to support the rich estuarine biodiversity of Elkhorn Slough.”
In summary, this pioneering study has demonstrated that the land acquisition and restoration projects of ESF have directly translated into improved water quality. We can assert with certainty that ESF’s and ESNERR’s forward thinking and dedication to our long-term mission and goals have made a measurable, positive difference. And our science and land management techniques continue to break new ground and set examples for land trusts nationwide.