Nathaniel B. Morse

Surprises and Insights from Long-Term Aquatic Data Sets and Experiments

long-term research on freshwater ecosystems provides insights that can be difficult to obtain from other approaches. Widespread monitoring of ecologically relevant water-quality parameters spanning decades can facilitate important tests of ecological principles. Unique long-term data sets and analytical tools are increasingly available, allowing for powerful and synthetic analyses across sites. long-term measurements or experiments in aquatic systems can catch rare events, changes in highly variable systems, time-lagged responses, cumulative effects of stressors, and biotic responses that encompass multiple generations. Data are available from formal networks, local to international agencies, private organizations, various institutions, and paleontological and historic records; brief literature surveys suggest much existing data are not synthesized. Ecological sciences will benefit from careful maintenance and analyses of existing long-term programs, and subsequent insights can aid in the design of effective future long-term experimental and observational efforts. long-term research on freshwaters is particularly important because of their value to humanity.

Assessment of Regional Variation in Streamflow Responses to Urbanization and the Persistence of Physiography

Aquatic ecosystems are sensitive to the modification of hydrologic regimes, experiencing declines in stream health as the streamflow regime is altered during urbanization. This study uses streamflow records to quantify the type and magnitude of hydrologic changes across urbanization gradients in nine U.S. cities (Atlanta, GA, Baltimore, MD, Boston, MA, Detroit, MI, Raleigh, NC, St. Paul, MN, Pittsburgh, PA, Phoenix, AZ, and Portland, OR) in two physiographic settings. Results indicate similar development trajectories among urbanization gradients, but heterogeneity in the type and magnitude of hydrologic responses to this apparently uniform urban pattern. Similar urban patterns did not confer similar hydrologic function. Study watersheds in landscapes with level slopes and high soil permeability had less frequent high-flow events, longer high-flow durations, lower flashiness response, and lower flow maxima compared to similarly developed watersheds in landscape with steep slopes and low soil permeability. Our results suggest that physical characteristics associated with level topography and high water-storage capacity buffer the severity of hydrologic changes associated with urbanization. Urbanization overlain upon a diverse set of physical templates creates multiple pathways toward hydrologic impairment; therefore, we caution against the use of the urban homogenization framework in examining geophysically dominated processes.

Removal of terrestrial DOC in aquatic ecosystems of a temperate river network

Surface waters play a potentially important role in the global carbon balance. Dissolved organic carbon (DOC) fluxes are a major transfer of terrestrial carbon to river systems, and the fate of DOC in aquatic systems is poorly constrained. We used a unique combination of spatially distributed sampling of three DOC fractions throughout a river network and modeling to quantify the net removal of terrestrial DOC during a summer base flow period. We found that aquatic reactivity of terrestrial DOC leading to net loss is low, closer to conservative chloride than to reactive nitrogen. Net removal occurred mainly from the hydrophobic organic acid fraction, while hydrophilic and transphilic acids showed no net change, indicating that partitioning of bulk DOC into different fractions is critical for understanding terrestrial DOC removal. These findings suggest that river systems may have only a modest ability to alter the amounts of terrestrial DOC delivered to coastal zones.

Effects of suburbanization on foodweb stoichiometry of detritus-based streams

Abstract.  Changes to nutrient loads may affect the stoichiometry of urban or suburban stream food webs. We quantified foodweb stoichiometry in 9 detritus-based headwater streams draining forested or suburban watersheds in northeastern, coastal Massachusetts (USA). We measured C, N, and P content (%C, %N, %P) and relative ratios (C∶N∶P) of basal food resources and macroinvertebrate consumers in each stream. Greater dissolved nutrient concentrations in suburban streams did not cause significant changes in overall elemental content (%C, %N, %P) of basal food resources, but their N∶P ratios decreased in high-nutrient streams, indicating that higher nutrients do affect food quality. The nutrient content of most macroinvertebrate taxa consuming these altered food resources was unaffected by suburban nutrient enrichment. However, some taxa deviated from strict homeostasis. Samples of these stoichiometrically variable taxa from the most enriched suburban streams had variable %N, a result suggesting that shifts in %P may not be the only means by which body stoichiometry is altered by nutrient enrichment. Moreover, many of the taxa with nutrient contents that differed across stream groups are typically more abundant in suburban than in forested streams, a result suggesting a potential link between consumer–resource stoichiometry and the tolerance of certain taxa for nutrient enrichment. Overall, our results are consistent with those of other studies on ecosystem properties or functions in urban streams in which the complex nature of urban effects does not always yield general patterns seen in less-affected systems.