Parsing spatial and temporal variation in stream ecosystem functioning

Abstract

The decomposition of organic matter is a fundamental ecosystem-level process that governs nutrient cycling, fuels ecosystems, and impacts our global climate. Despite the central importance of this process for ecosystems across the planet, little is known about how the capacity of ecosystems to decompose organic matter-that is, their decomposition potential-varies across time and space. Closing this gap is needed to provide baseline information on the dynamics of ecosystems, for tracking anthropogenic impacts, and for development of practical and efficient sampling procedures. For nine consecutive years during the months of July-August, we deployed an identical organic-matter decomposition assay in the same 26 temperate deciduous-forest streams (234 stream-years total) to evaluate the interannual and among-stream variation in the decomposition of organic matter. Decomposition rates (as k values) ranged widely across all stream-years (mean = 0.026, SD = 0.018, range = 0.0020-0.094). Interestingly, among-stream variation, expressed on a per-stream basis, was more than three times greater than interannual variation (expressed on a per year basis), explaining 75% and 22% of the overall variation in our dataset, respectively. Removing the effects of temperature by adjusting decomposition rates for degree days did not substantially impact this pattern (stream: 80% of variation, year: 17% of variation). Surprisingly, despite large differences in temperature among streams, temperature explained little variation in decomposition rates, pointing to the importance of other factors. When compared to the decomposition rates from stream sites across the planet, the rates presented here spanned 27.3% of this range, highlighting the diversity of decomposition rates that can be found in a relatively compact geographic area. From the perspective of using organic-matter decomposition as a bioassessment tool, this variation could limit the sensitivity of decomposition-based assays to human impacts, although study designs could be utilized to ameliorate this problem (e.g., those that stratify by geology). The results and dataset presented here are a needed step toward a more complete understanding of how ecosystem processes vary across time and space.

Multiple stressors mediate the effects of warming on leaf decomposition in a large regulated river

“…Although we observed an ~117% increase in saltcedar decomposition and attribute this acceleration to interactions among warming, litter quality, and a high abundance of mudsnails, it is worth noting that the magnitude of this change is comparable to interannual variability of litter breakdown observed in other studies (Mancuso et al, 2022). For example, Mancuso et al studied OM decomposition in 26 streams throughout northern Michigan over nine consecutive years and found that the rate of cotton‐strip decomposition varied as much as 2000% (0.002–0.05 k ) within a single stream.…”

Improving ecosystem health in highly altered river basins: a generalized framework and its application to the Mississippi-Atchafalaya River Basin

“…Although the technical ability to measure ecosystem metabolism has greatly advanced in recent years (Ferreira et al, 2020), such monitoring remains limited, especially across large spatial scales, because it is difficult to ensure comparability of measurement techniques (Brosed et al, 2022). Additionally, interpretation of site-specific results in terms of ecosystem health remains challenging (Mejia et al, 2018) and high spatial variability between sampling sites makes it difficult to synthesize results from specific sites to entire watersheds (Mancuso et al, 2022). For this reason, we decided to seek an alternative approach to monitoring ecosystem function, and turned instead to reviewing studies that have shown strong statistical relationships between landscape composition and pattern and various ecological processes (Qiu and Turner, 2015;Duarte et al, 2018;Qiu, 2019;Metzger et al, 2021).…”

Year-to-year variations have a more impact on leaf litter breakdown than the presence or absence of riparian vegetation in highland grasslands streams

“…On the other hand, highland grasslands often have natural open streams areas without riparian vegetation (Fernandes 2016). Therefore, understanding how spatial heterogeneity of gallery riparian zones act in highland grasslands stream systems is fundamental to understanding the dynamics and importance of leaf litter breakdown process and decomposer's community in ecosystems as a whole (Rezende et The rate of leaf litter breakdown and decomposer's community may changes from year to year in response to physical and chemical changes by environmental local alterations (Mancuso et al 2022). This temporal niche variability in local environmental characteristics may have a signi cant impact on the quantity and quality of leaf litter input (Peng et al 2018), affecting the decomposition process, and consequently, the availability of nutrients and aquatic biodiversity (Lodge and Cantrell 1995;Atkins et al 2017;Liu et al 2023).…”