Measuring and modeling seston uptake of restored reefs

摘要

A typical goal of oyster restoration projects is to enhance water quality because of increased water filtration rates by the oysters. However, the literature on the topic indicates that this is not always the case. There is a need to develop practical methods for predicting the impacts of restored molluscan shellfish populations on water quality. We developed a simplified, spreadsheet-based model to predict the percent of the total water column cleared of seston by suspension feeding bivalve molluscs: % Water Clearance = (A x B x C)/(D x E) x 100 where A = mean bivalve density (# ind/m2), B = mean individual clearance rate (m3/individual/h), C = bottom area of reef (m2), D = cross-sectional area of water column (m2), and E = mean water flow speed (m/hr). The variables typically can be easily measured (or estimated), except mean clearance rate, which is based on literature values. The major simplifying assumption is a completely mixed water column. Field tests thus far over oyster reefs (natural and developing), mussel reefs, and hard clam aquaculture beds indicate reasonably good agreement with model predictions when the major assumptions are met. Soon we will be using this approach in the field as a non-destructive method to assess the impact of filter-feeding as a surrogate for improved water quality with reef development. Using this technique we hope to be able to compare shallow, intertidal, and subtidal reefs across a large latitudinal range with different reef morphologies and environmental regimes.