Forest management influences the effects of streamside wet areas on stream ecosystems

Abstract

Riparian zones contain areas of strong hydrological connectivity between land and stream, referred to as variable source areas (VSAs), and are considered biogeochemical control points. However, little is known about whether VSAs influence stream communities and whether this connectivity is affected by forest management. To address this, we used multiple biotic and abiotic indicators to (1) examine the influence of VSAs on riparian vegetation and stream ecosystems by comparing VSA and non-VSA reaches and (2) explore how forest management may affect the influence of VSAs on stream ecosystems. We detected some significant differences between VSA and non-VSA reaches in the riparian vegetation (greater understory and lower tree density) and stream ecosystem indicators (greater dissolved organic matter aromaticity, microbial biomass, peroxidase activity and collector-gatherer density, and lower dissolved organic carbon concentrations, algal biomass, and predatory macroinvertebrate density), which suggests that VSAs may create a more heterotrophic ecosystem locally. However, we show some evidence that forest management activities (specifically, road density) can alter the influence of VSAs and eliminate the differences observed at lower forest management intensities, and that the most hydrologically connected areas seem more sensitive to disturbance. Therefore, we suggest that the heterogeneity in hydrological connectivity along riparian zones should be considered when planning forest harvesting operations and road building (e.g., wider riparian buffers around VSAs).

Are There Longitudinal Effects of Forest Harvesting on Carbon Quality and Flow and Methylmercury Bioaccumulation in Primary Consumers of Temperate Stream Networks?

“…In addition, Jonsson et al (2018) found that the autochthony of blackfly and caddisfly larvae was greater at sites with greater inputs from lakes and wetlands. In the present study, there were negative effects of percentages of EVSA, DOM1, and DOM2 in the linear models of percentage of algae in hydropsychid diets, which may be because EVSAs increase the delivery of terrestrial organic matter and reduce the relative availability of algae to consumers (Erdozain et al, 2020).…”

“…The model for aqueous MeHg in the present study indicated a positive effect of DOM1 (explained by HIX and E2E3, which are indicators of DOM humification and aromaticity, respectively; Table 5), concurring with other positive relationships between aqueous MeHg and DOM quality (see Lescord et al, 2018; Tsui & Finlay, 2011). Surprisingly, there was a nonsignificant negative effect of percentage EVSA on aqueous MeHg in linear models; this was unexpected because EVSAs generally promote transport of DOM (Erdozain et al, 2020) and may also represent ideal areas for methylation to occur (Bishop et al, 2009). The lack of effects of percentage EVSA on aqueous MeHg observed may be because EVSAs were largely within the no‐harvest buffer zones and therefore not subject to disturbance.…”

“…A key component of the carbon cycle in headwater streams is DOM, and its quality and quantity are affected by forest harvesting through its alterations of water table levels and associated aerobic/anaerobic conditions (Erdozain et al, 2018(Erdozain et al, , 2020Kiikkilä et al, 2014). Molecules of DOM vary widely in structure, weight, protein content, aromaticity, and lability (i.e., the quality of DOM), often reflecting source, processing time, biological activity, and hydrologic connectivity (Ravichandran, 2004).…”

Measuring changes in financial and ecosystems service outcomes with simulated grassland restoration in a Corn Belt watershed

“…Furthermore, in the productivity scenario the in-field costs of grass harvest, baling and on-site transportation and storage would likely be highly variable due to the heterogeneous scale, shape and patchy nature of the biomass systems presented (Nair et al, 2017). Likewise, accessibility in riparian areas can be complicated by moisture conditions during harvest periods and the care often needed to minimize harvest impact in hydrologically sensitive areas (Erdozain et al, 2020). Ultimately the spatial fragmentation of the biomass systems presented in our study would likely carry additional, but unaccounted for logistical and or environmental costs associated with harvesting and on-site handling of biomass materials (Ferrarini et al, 2017).…”

Understanding the effects of forest management on streams and rivers: A synthesis of research conducted in New Brunswick (Canada) 2014–2018

“…Such a decrease slows down the recycling of nutrients such as carbon and nitrogen. Regarding the importance of streamside wet areas, there were some differences between in-stream indicators near wet and dry sites, suggesting that these streamside areas created distinct local ecosystems (Erdozain et al 2020). Moreover, the study showed that forest management activities (specifically roads) can diminish the differences in several indicators (such as microbial biomass and activity) between stream sections draining wet and dry sites, leading to lower diversity in stream habitats (i.e., habitat homogenization) with implications for biodiversity at the stream level.…”