The Southern Everglades mangrove ecotone is part of a highly oligotrophic, P-limited estuarine ecosystem. The wetland vegetation in this region is comprised mostly of dwarf red mangrove spanning the oligohaline zone between the freshwater marshes to the north and Florida Bay to the south. The hydrology of the region is wind and runoff-dominated with a small tidal component and is characterized by a strong seasonal pattern in rainfall and discharge from numerous creek systems.

Global climate change is emerging as the single most important environmental issue of the 21st century. The direct and indirect effects of climate change on terrestrial and aquatic ecosystems are highly complex and poorly understood. High elevation watersheds can be a useful unit for studying climate-induced effects because they are sensitive to global change processes and may serve as a bellwether for more resistant ecosystems of higher order watersheds.

One of the overarching conclusions from the recent LINX II stream ¹⁵N tracer experiments was that direct denitrification tends to explain only a minority of nitrate (NO₃^-) loss from the water column (median, 16%: Mulholland et al. 2008, Nature 452: 202). The balance of “retained” NO₃^- (measured as ¹⁵N-NO₃^- lost from stream water) appears to have been assimilated rather than denitrified, and may eventually be released back to the stream.

Phosphorus (P) is often limiting in aquatic ecosystems. The quantity of available P is often determined by sediment binding and release processes. We obtained 32 sediment samples from shallow freshwater ecosystems in Southwest Michigan. Sediment cores were separated into consolidated and flocculent strata for analysis of percent organic matter, total sediment phosphorus (TP), and HCl-extractable iron (HCl~Fe). Sediment TP ranged from 110-3348 ugP/gdw, with an average of 1052 ugP/gdw.

Permafrost plays an important role in shaping the chemistry of streams by restricting subsurface flows through catchments to soils. During the summer thaw of soil, subsurface flows migrate through deeper soil horizons presumably resulting in seasonal shifts in the inputs of carbon and nitrogen to the streams. Within streams, the extent of the hyporheic zone may also shift with seasonal thaw. Hyporheic zones have high mineralization and nitrification rates; thus expansion of the hyporheic zone throughout the season has important implications for stream chemistry.