David C. Richardson

Stream restoration strategies for reducing river nitrogen loads

Despite decades of work on implementing best management practices to reduce the movement of excess nitrogen (N) to aquatic ecosystems, the amount of N in streams and rivers remains high in many watersheds. Stream restoration has become increasingly popular, yet efforts to quantify N-removal benefits are only just beginning. Natural resource managers are asking scientists to provide advice for reducing the downstream flux of N. Here, we propose a framework for prioritizing restoration sites that involves identifying where potential N loads are large due to sizeable sources and efficient delivery to streams, and when the majority of N is exported. Small streams (1st–3rd order) with considerable loads delivered during low to moderate flows offer the greatest opportunities for N removal. We suggest approaches that increase in-stream carbon availability, contact between the water and benthos, and connections between streams and adjacent terrestrial environments. Because of uncertainties concerning the magnitud...

Communicating with the public: opportunities and rewards for individual ecologists

Many ecologists are interested in communicating science to the public and addressing societal concerns about environmental issues. Individual ecologists need to consider whether, when, and how this should be done. We propose that public outreach activities can be beneficial for ecologists at all stages of their career. There are diverse opportunities for such involvement, and these can vary enormously in terms of time and expertise required. Trends within the science of ecology, especially research focused on social-ecological systems, are likely to promote increased interactions with stakeholders and policy makers. To be effective in these interactions, ecologists should consider new approaches to communication and be aware of the potential roles scientists can play in public policy debates. Professional ecologists need to engage with non-scientific audiences; a review of such activities should be included in considerations for promotion, recognition, and awards, while also acknowledging variations in the inclinations and abilities of individual scientists. There are, however, few current standards for how much time ecologists should commit to public outreach, how time allocation might change over a career, or how to evaluate the quality of such activities. We ask ecologists to consider ways to evaluate the quality of interactions with the public and how to reward these efforts appropriately.

Ecosystem Effects of a Tropical Cyclone on a Network of Lakes in Northeastern North America

Here we document the regional effects of Tropical Cyclone Irene on thermal structure and ecosystem metabolism in nine lakes and reservoirs in northeastern North America using a network of high-frequency, in situ, automated sensors. Thermal stability declined within hours in all systems following passage of Irene, and the magnitude of change was related to the volume of water falling on the lake and catchment relative to lake volume. Across systems, temperature change predicted the change in primary production, but changes in mixed-layer thickness did not affect metabolism. Instead, respiration became a driver of ecosystem metabolism that was decoupled from in-lake primary production, likely due to addition of terrestrially derived carbon. Regionally, energetic disturbance of thermal structure was shorter-lived than disturbance from inflows of terrestrial materials. Given predicted regional increases in intense rain events with climate change, the magnitude and longevity of ecological impacts of these storms will be greater in systems with large catchments relative to lake volume, particularly when significant material is available for transport from the catchment. This case illustrates the power of automated sensor networks and associated human networks in assessing both system response and the characteristics that mediate physical and ecological responses to extreme events.

The role of native riparian tree species in decomposition of invasive tree of heaven (Ailanthus altissima) leaf litter in an urban stream

Abstract Increasingly, interactions between human and natural systems centre on the multi-scale restoration of ecosystems. Humans rely on ecosystem services provided by streams, yet human activities degrade water quality worldwide. Re-planting streamside vegetation is a common restoration practice, since trees reduce runoff and stabilize banks. But does riparian tree biodiversity matter? Detrital inputs from riparian vegetation impact in-stream processes, e.g., leaf decomposition. Since the increasing distribution of invasive plant species alters the structure of streamside forest communities, input of invasive litter to streams could alter such processes. We followed decomposition rates of the invasive tree of heaven (Ailanthus altissima, TOH) and 6 native leaf species in an urban stream and complemented this effort with laboratory feeding experiments employing the same treatments and 2 common aquatic detritivores. TOH breakdown was rapid, exceeding native leaf decay. Mixing TOH with native species reduced its decay compared to TOH alone; however, the feeding study demonstrated that detritivores preferred TOH over native species. Subsequent estimates of species-specific structural integrity revealed TOH poorly resisted breakage. The relatively tougher nature of native species may slow TOH breakdown by armouring the invasive litter against the highly variable flow regime characteristic of urban streams. The presence of native riparian tree species may mediate how invasive trees decompose in human-impacted streams.

Intra- and inter-annual variability in metabolism in an oligotrophic lake

Lakes are sentinels of change in the landscapes in which they are located. Changes in lake function are reflected in whole-system metabolism, which integrates ecosystem processes across spatial and temporal scales. Recent improvements in high-frequency open-water metabolism modeling techniques have enabled estimation of rates of gross primary production (GPP), respiration (R), and net ecosystem production (NEP) at high temporal resolution. However, few studies have examined metabolic rates over daily to multi-year temporal scales, especially in oligotrophic ecosystems. Here, we modified a metabolism modeling technique to reveal substantial intra- and inter-annual variability in metabolic rates in Lake Sunapee, a temperate, oligotrophic lake in New Hampshire, USA. Annual GPP and R increased each summer, paralleling increases in littoral, but not pelagic, total phosphorus concentrations. Storms temporarily decoupled GPP and R, resulting in greater decreases in GPP than R. Daily rates of GPP and R were positively correlated on warm days that had stable water columns, and metabolism model fits were best on warm, sunny days, indicating the importance of lake physics when evaluating metabolic rates. These metabolism data span a range of temporal scales and together suggest that Lake Sunapee may be moving toward mesotrophy. We suggest that functional, integrative metrics, such as metabolic rates, are useful indicators and sentinels of ecosystem change. We also highlight the challenges and opportunities of using high-frequency measurements to elucidate the drivers and consequences of intra- and inter-annual variability in metabolic rates, especially in oligotrophic lakes.

Using Large Data Sets for Open-Ended Inquiry in Undergraduate Science Classrooms

National Science Foundations Transforming Undergraduate Education in Science, Technology, Engineering, and Mathematics (TUES) [1245707]; National Association of Geoscience Teachers (NAGT)

Reconstructing a trophic cascade following unintentional introduction of golden shiner to Lake Minnewaska, New York, USA

Abstract Introductions of new species may rapidly and irreversibly change lake food webs and ecosystems, but such events are rarely documented as a result of inadequate pre-invasion monitoring. We examined the unintentional introduction of a fish species, golden shiner (Notemigonus crysoleucas), a small planktivorous minnow, to Lake Minnewaska, New York State, USA. We predicted that the introduction had caused a trophic cascade resulting in increased algal biomass and decreased water clarity mediated by decreasing zooplankton size and biomass. This prediction was confirmed using limited monitoring data through comparisons made between “control” lakes (both with fish in Mohonk Lake and without fish in Lake Awosting) and the “intervention” lake (Minnewaska).

History of Fish Presence and Absence Following Lake Acidification and Recovery in Lake Minnewaska, Shawangunk Ridge, NY

Abstract Lake acidification is a major problem in northeastern US lakes that can control fish presence or absence. We examined the history of fish populations in Lake Minnewaska, in eastern New York. We examined historical documents and found that Lake Minnewaska was fishless from 1922–2008 because of high lake-acidity. Following 30 years of recovery from acidic conditions, Notemigonus crysoleucas (Golden Shiner), a small minnow species, was introduced in 2008 and quickly proliferated, peaking at∼15,000 individuals in 2013. In 2012, the piscivorous species Micropterus salmoides (Largemouth Bass) was introduced, and the minnow population was effectively removed by 2014. We present a conceptual model of the history of fish in Lake Minnewaska as fish disappeared and reappeared over 100 years as a consequence of acid rain and human introductions.

Watershed management and underlying geology in three lakes control divergent responses to decreasing acid precipitation

Abstract In northeastern North America, acidification of precipitation and freshwater ecosystems is due to increased anthropogenic emissions of sulfate (SO42−) and nitrogen oxides (NOx). Legislative changes (e.g., the 1990 Clean Air Act Amendment) have resulted in decreasing emissions and increasing precipitation pH. We hypothesized that precipitation pH increased and regional improvements in acid precipitation resulted in increasing pH levels in our study lakes – Lake Minnewaska, Lake Awosting, and Mohonk Lake, on the Shawangunk Ridge, New York, USA – but the rates of change would be dependent on underlying geology and watershed management. Precipitation pH increased from 4 in 1976 to >5 in 2015. Our 3 study lakes had increasing pH, although at different rates from changes in precipitation pH and compared to each other. Several factors likely control the differences in lake acidity improvements. Mohonk has remained neutral because of an exposed shale inlier in the lake that buffers the acidic precipitation. The bedrock under Awosting and Minnewaska is quartz-conglomerate with little buffering capacity. Changes in Awosting seem to be closely linked to precipitation pH recovery; however, the pH in Minnewaska has increased above biologically meaningful levels because of eroding shale recreational trails around the lake, a finding supported by water chemistry trends. Across this region and around the world, the rate of recovery from acid precipitation and decrease in lake acidity in this region can affect the return of acid-sensitive freshwater ecological communities.