Hydrogeomorphological Controls On Stream Chemistry And Aquatic Biota In The Catskill Mountains, New York State
Traditional Darcy-based models have not been providing satisfactory answers for watershed scientists working in complex landscapes and new methods are thus being developed. Ideally these new methods would characterize discharge patterns, estimate stream chemistry, and can be transferrable between complex and heterogeneous watersheds. In this dissertation, we develop two such methods by relating hydrologic and geomorphologic (or "hydrogeomorphologic") properties to stream chemistry, biota and (preferential) flow patterns. The research is carried out in two different, well-studied watersheds in the Catskill Mountains, New York State: Neversink River and Town Brook. The 176 km2 Neversink River watershed has a detailed discharge, chemistry, and biotic data for nested sub-watersheds (0.2 to 160 km2) that are affected by acid rain. The results from the Neversink River watershed showed that baseflow stream acid buffering chemistry (ANC values and Ca2+ concentrations) was reduced in subwatersheds that were steeper or had more stream channels. Although speculative, we believe that long-term flushing of base cations from the shallow soils during storm runoff events reduces the acid buffering chemistry during baseflow. A simple geomorphologic relationship, based on mean slope and stream channels per area, was strongly correlated to populations of aquatic biota (macroinvertebrate, periphytic diatom, and fish) in "ungaged" sub-watersheds where discharge was not measured. Town Brook watershed (2.5 km2) was investigated to determine the sources and flowpaths of water during nine rainfall events from April 2007 to October 2007. A combination of hydrometric, chemical, and isotopic data sets was measured and surface saturation maps were developed. The results suggested that during precipitation events greater than 1 cm, hill side saturation areas caused by groundwater springs and soil pipes were a significant runoff source. The properties commonly used to infer surface saturation areas in Town Brook (i.e. slope, upslope area, and/or soil transmissivity) predicted general spatial patterns, but were insufficient to estimate surface saturation at the smallest scales measured ( less than 100 m2). The success of hydrogeomorphologic properties in estimating stream acid buffering chemistry and watershed saturation patterns in the two Catskill watersheds suggest that simple alternatives to traditional Darcy-based predictions may be applicable under certain conditions.
dissertation or thesis