Stream size and human influences on ecosystem production in river networks

Abstract

Abstract. The quality and amount of productivity plays a central role in determining community structure and biogeochemical dynamics in ecosystems. Humans have altered river ecosystems in multiple ways that are likely to influence annual rates of ecosystem productivity and metabolism, but the net affects of such modifications on these processes are poorly known, especially at annual scales. An analysis of annual, whole ecosystem productivity for over 200 streams and rivers shows that human activities shift the amount, quality, and spatial distribution of production in river networks via enrichment of resources that limit autotrophic production. Human actions increased primary production to a greater degree than heterotrophic respiration, shifting streams (i.e., sites ,100 km 2 watershed area) toward greater autochthony. Whereas human activities change multiple aspects of environmental conditions in streams, and often result in habitat degradation, reduction in biodiversity, and elevated contaminants, these analyses show that primary and secondary productivity of strongly impacted streams increased by over 600% relative to reference (pristine/lightly modified) sites due to increased resource availability and quality. A human-driven increase in autotrophic-based production is thus likely a major factor in ongoing global shifts in biodiversity, trophic dynamics and element cycling in streams.

Metabolism, Gas Exchange, and Carbon Spiraling in Rivers

“…The 4 rivers in the Midwestern US had moderate rates of metabolism with low variation among them. Despite evidence showing that GPP can increase as a function of stream or river size (Figure 3) (Finlay 2011), variation in metabolism among rivers was large enough that rivers have no characteristic rate of metabolism.…”

Catchment properties predict autochthony in stream filter feeders

“…Nevertheless, forestry seemed to exert a stronger and more general influence on the resource base of filter feeders than did agriculture, which may be expected as forestry is much more widespread (i.e., represents a stronger gradient) than agriculture in the study region. Regardless, the associations between filter-feeder diets and both types of land use further emphasized that modifications in terrestrial environments can cause deviations from the expected relationship between stream size and autochthony versus allochthony in stream consumers (Finlay, 2011;Stenroth et al, 2015;Jonsson & Stenroth, 2016). In fact, when variability of a range of environmental factors was taken into account, stream size (assuming a positive relationship with drainage area) explained no variation in autochthony in the black fly larvae, and there was even a negative relationship between stream size and autochthony in the caddisfly larvae.…”

“…In streams, food-web autochthony is predicted to be lowest in the headwaters and increase downstream (Vannote et al, 1980;Collins et al, 2016), and there should, therefore, be a simultaneous increase in secondary production downstream (Finlay, 2011;Kelly et al, 2014). However, in small, heterotrophic streams, a peak in secondary production-and therefore, consumer allochthony-can occur soon after the seasonal input of riparian plant litter, which therefore, often coincides with an increased abundance of macroinvertebrate detritivores (Richardson, 1991;Wallace et al, 1999).…”

Influence of watershed‐climate interactions on stream temperature, sediment yield, and metabolism along a land use intensity gradient in Indonesian Borneo

“…These include stream aspect and size, soil type and nutrient status, bedrock characteristics, and the degree of surface-subsurface water exchange [Findlay, 1995;Finlay, 2011;Mohamoud, 2004]. Land conversion location and pattern also affect stream hydrology [Allan, 2004;Ziegler et al, 2006].…”

“…Croplands span~12% of the world's land surface, and increased food demand from altered diets and growing population is expected to lead to crop expansion and intensification, especially within tropical regions [Foley et al, 2011;Tilman et al, 2011]. Because rivers are spatially nested complex systems [Allan, 2004], the influence of agricultural land use change on tropical freshwater streams depends on multiple interactions among physical, chemical, and biological conditions occurring across spatial and temporal scales [Ponette-González et al, 2010a, 2010bUriarte et al, 2011].…”