Assessing the impacts of anthropogenic acidification on autotrophic stream biofilms using pulse amplitude modulation fluorometry

Pulse amplitude modulation fluorometry (PAM) has not been extensively studied as a rapid assessment tool for acidification in freshwater biofilms. In this project I focused on two types of anthropogenic acidification to determine the efficacy of PAM as a rapid health assessment tool for impaired freshwater streams by using responses to non-visible algal stress. Acidification alters algal community composition such that only acid- and metal-tolerant species thrive. Metal and acid impairment affects primary production by blocking electron transport and reducing the amount of NADP and ATP created in non-acidophilic algae, potentially lowering photosynthetic capacity of the overall algal community. PAM fluorometry allows for the rapid assessment of photosynthetic potential in algae and other plants.  The purpose of this study was to determine how well PAM can assess the impacts of anthropogenic acidification on algal physiology in algal-dominated stream biofilms. I used a Walz MiniPAM II to perform rapid light curves and measure Fv/Fm on periphyton in 13 streams throughout central Pennsylvania, including unimpaired streams as well as streams impaired by 1) acid mine drainage or 2) acid deposition. I also measured water chemistry and algal biomass in each stream. The results of this study demonstrate pulse amplitude modulation fluorometry to be an effective tool for assessing algal stress in acid impaired streams. Overall, acidified streams had low biomass and productivity. Based on Akaike Information Criterion (c), log maximum electron transport rate, (a measure of maximum potential photosynthesis), was best described by a model that included pH and log chlorophyll a. This model was the most parsimonious model describing the relationships between the observed PAM parameters and measures environmental variables. Although this study demonstrated that PAM was effective at assessing the effects of high metal concentrations and low pH on algal communities in acid-impaired streams, further study is needed to determine whether PAM is effective at assessing the effects of other impairments, such as elevated nutrients and other contaminants.