The LTER is conducting annual monitoring of Algae, Chlorophyll a, benthic organic matter, and benthic inorganic matter in order to document baseline stream characteristics. These data may be used to examine effects of disturbances such as hurricanes on stream ecosystems.
Our long-term data shows how algal primary producers respond to disturbance. The resistance and resilience of primary producer biomass to different types of disturbance (drought and high discharge) is affected by the relative degree of top-down control by different stream macroconsumer assemblages representative of low-order streams draining LUQ. The LUQ stream algae dataset is unique among LTER sites because of its long-term nature and because it provides integrated quantitative measures of algal standing crop (AFDM, chlorophyll a) at a relatively large scale (1 km stream reaches) and is not just ‘snapshot’ sampling at one location. We also sample 2 x per year with more intensive sampling during droughts (5-6 x per year).
We found dramatically lower levels of algal standing crop during peak drought conditions in 2015. In Prieta, algal standing crop was 16-22 fold lower in pools and 11 -18 fold lower in riffles, compared to the long-term summer average - - - assumedly due to concentrated grazing of large numbers of omnivorous shrimps in a small volume of water. In Bisley-3, algal standing crop was 5-9 fold lower in pools and 2-6 fold lower in riffles compared to the long-term (2003-14) summer average. Inorganic sediments in pools were highly variable and ~2 fold greater in riffles compared to the long-term summer average.
We also measured extremely high spatial variability in conductivity and solute chemistry between pools in Prieta and Bisley-3 in July- August 2015 due to the lack of flow in riffles connecting pools. Conductivity in both streams was 1.5 - 1.6 fold greater than mean conductivity over the last decade (2002-12).