Abstract
Excess sediment and nutrient runoff from land-based human activities are considered serious threats to coastal and marine ecosystems by most conservation practitioners, resource managers, fishers, and other “downstream” resource users. Deleterious consequences of coastal runoff, including eutrophication and hypoxia, have been observed worldwide. Literature on integrated coastal management offers numerous methods to address land-based activities that generate runoff, but many of these approaches are time- and resource-intensive. Often, high-level conservation managers have few tools to aid in decisions about whether land-based threats that generate runoff are of sufficient concern to warrant further investment in planning and management interventions. To address this decision-making process, we present a decision tree that uses geophysical and ecological characteristics to sort any marine coastal ecosystem into a category of high, moderate, low, or minimal risk from the land-based threats of nutrient and sediment runoff. By identifying situations where runoff could influence biodiversity or ecosystem services, the decision tree assists managers in making informed and standardized decisions about when and where to invest further efforts in integrated land-sea planning. We ground-truth the decision tree by evaluating it in five very different regions and conclude the tree classifies regions similarly to the existing literature that is available, but based on less information. Recognizing that the decision tree only encompasses environmental variables, we also discuss approaches for interpreting the decision tree’s outputs in local social and economic contexts. The tree provides a tool for conservation managers to decide whether the scope of their work should include land-sea planning.
Highlights
Coastal and marine ecosystems experience anthropogenic pressures at scales from local to global, many of which originate beyond the coastal oceans (Halpern et al, 2008b, 2012)
To address the gap between the land-sea planning literature and resource-limited regions, we developed a decision tree to help natural resource or conservation managers decide whether land-based human activities need to be included within the scope of their endeavors (Figure 1)
We drew on hydrology and coastal ecology to identify a set of variables that influence whether human activities produce elevated nutrient or sediment loads in a watershed, how that load is transported to the coastal oceans, and how coastal ecosystems respond (Vitousek et al, 1997; Carpenter et al, 1998; Cloern, 2001; Mayorga et al, 2010; Fabricius, 2011; Milliman and Farnsworth, 2011)
Summary
Coastal and marine ecosystems experience anthropogenic pressures at scales from local (e.g., fishing, coastal development) to global (e.g., warming, acidification, rising seas), many of which originate beyond the coastal oceans (Halpern et al, 2008b, 2012). Practitioners are often faced with coastal management and planning decisions without a systematic process to assess the relative importance of land-based impacts. Gathering sufficient data for a single region to quantitatively determine the ecological, economic, and social impacts of anthropogenic runoff is extremely time- and resource-intensive, and beyond the capacity of most coastal marine managers worldwide. This study seeks to provide a rapid tool for managers in data-poor coastal marine regions to determine whether costly land-sea planning is necessary, based on the threat of anthropogenic nutrient and sediment loading. Among the regions left in this level, those that both experience rapid mixing due to upwelling, and likely have marine ecosystems that are adapted to a naturally nutrient-rich environment, are considered at less risk and assigned the “land-based drivers minimal” category.
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