Robert M. Northington

Aquatic Insect Ecology

Publisher Summary Aquatic insects are abundant in most freshwater habitats and often exhibit high diversity. In aquatic food webs, they serve as food items for nearly the full range of vertebrate and invertebrate predators, and many function as predators themselves. This chapter provides a brief overview of: constraints on aquatic insect species diversity, life history, and community structure; the role of aquatic insects in ecosystem processes; the impact of land use, climate change, and disturbances on their communities; and the utility of aquatic insects in biomonitoring studies. The review encompasses both lentic and lotic habitats, as well as a brief coverage of saline habitats. The discussion is placed in the context of how physical and life history factors constrain the distribution and abundance of aquatic insects, thereby altering communities and ecosystem function.

Recent decrease in DOC concentrations in Arctic lakes of southwest Greenland

A key indicator of changes in the terrestrial carbon cycle is shifting dissolved organic carbon (DOC) concentrations in surface waters. Arctic permafrost holds twice as much C as the atmosphere, thus recent warming and changes in atmospheric deposition to the region raise the need for a better understanding of how DOC is changing in arctic surface waters. In Kangerlussuaq, Greenland, lakewater DOC concentrations declined by 14 to 55% (absolute changes of 1 to 24 mg L-1) between 2003 and 2013, without significant changes in quality. Lakewater sulfate concentrations, but not chloride or conductivity, increased. These results suggest that, similar to processes that have occurred at northern mid-latitudes, increases in soil ionic strength as a result of sulfate enrichment may be linked to declining surface water DOC concentrations. Such enrichment may be occurring with enhanced non-sea-salt sulfate deposition. Our results reveal that rapid changes are occurring in the carbon cycle of this region of southwest Greenland.

Benthic secondary production in eight oligotrophic arctic Alaskan lakes

Abstract Across aquatic ecosystems, benthic secondary production generally is thought to be limited by autochthonous primary production. We estimated secondary production in 8 oligotrophic arctic lakes of varying morphometric characteristics for which we also had estimates of pelagic and benthic primary production during the summer of 2001. Four of the lakes supported similar communities of fish, and 4 were fishless. The size–frequency method was used to calculate cohort production interval (CPI)-corrected lake benthic secondary production and production to biomass (P:B) ratios for all taxa in all lakes. Taxa examined from sediment samples included Baetis spp., Grensia praeterita, and larval chironomids. Larval chironomids had the greatest secondary production overall. Whole-lake benthic secondary production ranged from 1.02 to 20.52 g dry mass m−2 y−1. No significant relationship or trend was found between benthic secondary production and primary production (whole-lake, benthic, or pelagic). A stronger trend (p  =  0.2) suggested higher benthic secondary production in fishless lakes than in lakes with fish, but within fishless lakes, no pattern was found that suggested autochthonous control of benthic secondary production. Our study is unique in that we examined multiple oligotrophic lakes and demonstrated that the secondary production of benthic fauna was, at most, weakly related to autochthonous primary production. This result is in contrast to the commonly accepted paradigm that autochthonous production limits secondary production. We suggest that allochthonous organic matter sources were very important for supporting secondary production in these oligotrophic arctic lakes.

Response of stream salamanders to experimental drought in the southern Appalachian Mountains, USA

Droughts act as significant disturbances to freshwater animals and their ecosystems. Given the impending threat of more frequent and persistent droughts because of global climate change, the lack of data on the responses of many aquatic animals to drought is a cause for concern. This study examined the body condition of the most commonly detected species (Desmognathus quadramaculatus) and abundance of commonly found species after two years of experimental drought in two first-order streams in the southern Appalachian Mountains. Our results indicated negative effects of drought on the stream salamander community. The body condition of D. quadramaculatus larvae in experimental drought transects was significantly lower than larvae captured in control reaches, which may have resulted from lower macroinvertebrate production in experimental reaches. Additionally, larval D. quadramaculatus abundance declined 47% in experimental drought transects, and Eurycea wilderae larvae and D. ocoee adults were 70% less likely to be captured in experimental stream transects. Our findings contribute additional evidence that stream plethodontids have little resistance to drought. With extended droughts resulting from climate change more likely in the future, more research is necessary to determine if reduced body condition, production, and lowered abundance have effects on long-term population viability.

Use of allochthonous and autochthonous carbon sources by Chironomus in arctic lakes

(2010). Use of allochthonous and autochthonous carbon sources by Chironomus in arctic lakes. SIL Proceedings, 1922-2010: Vol. 30, No. 9, pp. 1321-1325.

Nutrient limitation status of Arctic lakes affects the responses of Cyclotella sensu lato diatom species to light: implications for distribution patterns

Changing environmental conditions in the Arctic have caused widespread but disparate changes in the relative abundances of diatoms in the Cyclotella sensu lato group since 1850 across Arctic lakes. To better understand the mechanisms behind these species changes, we investigated how the nutrient limitation status of a lake alters the responses of three common Cyclotella sensu lato taxa to light. To assess this, we collected source water with the natural phytoplankton assemblages from lakes in southwest Greenland with different nutrient limitation status (phosphorus (P)-limited or nitrogen & phosphorus (N&P) co-limited). The responses of Lindavia bodanica, Lindavia radiosa, and Discostella stelligera to light levels (low, moderate, or high) and nutrients (limited or replete) were tested using a factorial design. The vertical distributions of these taxa across 20 lakes of varying nutrient limitation status and water transparency were also assessed. We found that light affected Cyclotella growth rates, cell densities, and distribution patterns differently depending on lake nutrient limitation status. L. bodanica fared best at low light under P-limitation, and at high light under N&P co-limitation, while the pattern was generally opposite for D. stelligera. For L. radiosa, regardless of nutrient limitation status, moderate-to-high light was important, with this species absent from lakes with lower light conditions. This study reveals that environmental change affects these species via complex interactions between nutrient and light availability, and helps to clarify some of the complex distribution patterns of planktonic diatom taxa found in lakes of many areas around the Arctic as well as at lower latitudes.

Stable Isotopes in Stream Food Webs

Stable isotope analysis has become a common tool for studying stream food webs and for testing hypotheses about stream ecosystem processes and stressors that may affect the structure of the food web or resources available to consumers. In this chapter, we provide a brief discussion of use of natural abundances of stable isotopes to study stream food webs, including a primer on stable isotope terminology, fractionation processes that govern differential cycling of stable isotopes of the same element, and some of the applications of the specific elements most often commonly used for stable isotope studies in stream ecosystems. Our objectives are to illustrate a generalized method ( Basic Method ) for characterizing and comparing stream food webs using δ 13 C and δ 15 N, and three more advanced experimental approaches ( Advanced Methods 1–3 ) for examining specific questions or hypotheses about resource use in stream food webs using δ 13 C, δ 15 N, and δD.

Factors Controlling Methane in Arctic Lakes of Southwest Greenland

We surveyed 15 lakes during the growing season of 2014 in Arctic lakes of southwest Greenland to determine which factors influence methane concentrations in these systems. Methane averaged 2.5 μmol L-1 in lakes, but varied a great deal across the landscape with lakes on older landscapes farther from the ice sheet margin having some of the highest values of methane reported in lakes in the northern hemisphere (125 μmol L-1). The most important factors influencing methane in Greenland lakes included ionic composition (SO4, Na, Cl) and chlorophyll a in the water column. DOC concentrations were also related to methane, but the short length of the study likely underestimated the influence and timing of DOC on methane concentrations in the region. Atmospheric methane concentrations are increasing globally, with freshwater ecosystems in northern latitudes continuing to serve as potentially large sources in the future. Much less is known about how freshwater lakes in Greenland fit in the global methane budget compared to other, more well-studied areas of the Arctic, hence our work provides essential data for a more complete view of this rapidly changing region.