Rapid assessment of headwater streams

Posted on July 2, 2014


Because headwater streams can remain dry for long periods of time, it’s traditionally been assumed that their ecological benefits are relatively low. However, in recent years it’s been recognised that headwater streams play an important role in key ecosystem processes such as organic matter transport, sediment capture, temperature control and flow regulation. This re-evaluation has prompted interest in the activities of producers, consumers and decomposers in removing, altering and transporting materials in headwater systems. Reliable techniques are available for the assessment of ecosystem processes in headwater streams: for example, litter leaf fall is used as a proxy for nutrient / organic input, and leaf decomposition is used as a measure of nutrient processing. However, there’s a demand among natural resource managers for less time-consuming procedures that can be incorporated into routine surveys. American researchers gauged how well a rapid-assessment index (Functional Capacity Index, or FCI) reflected ecosystem function in ten West Virginian headwater catchments variously affected by agriculture, mining and forestry activities. FCI values were calculated from on-site ratings of fine sediment, large wood, detritus, tree diameter and landuse, and then plotted against estimates of leaf fall and leaf decomposition. Leaf fall was measured using leaf traps, and leaf decomposition was assessed by filling PVC mesh bags with leaves collected at the site and measuring the loss in dry weight and nutrient content over a six month period. Local trees included tulip tree, American sycamore, magnolias, maples and oaks . The FCI index scaled with the input and rate of processing of nutrients, both of which were higher in the less disturbed catchments. In contrast, the FCI score had a significant negative relationship with the stream loading of dissolved nutrients and suspended sediment, which were higher at the most disturbed sites. Therefore, although streams in disturbed catchments received more nutrients overall, fewer of those nutrients originated from leaf fall, and in altered catchments decomposer communities were less efficient at processing leaf fall nutrients. These results suggest that rapid assessment techniques can provide a reliable indication of ecosystem function in headwater streams. Rapid assessment methods are also economical: in the present study, they demanded only 10% of the time and less than 3.5% of the funds required by standard assessment techniques.

Reference: Berkowitz, J.F. et al. 2014. Investigation of biogeochemical functional proxies in headwater streams across a range of channel and catchment alterations
Environmental Management 53, 534–548. http://download.springer.com/static/pdf/785/art%253A10.1007%252Fs00267-013-0199-1.pdf?auth66=1404263137_ad8c8a29a03699b3e7cbda6b8275aa30&ext=.pdf

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