Cotton-strip Assay Research Articles

Field evaluation of the cotton-strip assay for quantifying decomposition rates in extensive green roof substrates

Extensive green roof (EGR) substrates and vegetation layer are critical components to ensure EGR multifunctionality. However, little is known on EGR substrate biological functioning, especially nutrient cycling that is crucial for supporting life in soils. This work aimed at investigating for the first time the effectiveness of an affordable and easy-to-use standardized method, the cotton-strip assay, to assess decomposition rates in ten-year old EGR. Three metrics were evaluated following 34–110 days of cotton-strip incubation into substrates: tensile strength, weight and surface area losses. Tensile strength loss was the most sensitive index after 34 days while weight loss over 110 days confirmed elevated decomposition rates in EGR substrates compared to gravel rooftop or common urban park soil. This could be related to positive influence of slightly acidic pH and vegetation cover. Finally, semi-intensive but thin green roof substrates may be an alternative to intensive ones to sustain ecological processes supporting long-term vegetation growth, as long as there is no net carbon loss. Moreover, broader assessment of decomposition into different green roof substrates configurations could pave the way for a better understanding of green roof ecosystems as a whole and the design of more resilient green infrastructures.

Microplastics are transferred by soil fauna and regulate soil function as material carriers

The ecotoxicological effects of microplastics, a new and widespread ecosystem pollutant, have been extensively reported. However, it remains unclear whether soil fauna transfer microplastics and whether migration behaviours influence subsequent ecological functions in terrestrial ecosystems. We investigated the transfer patterns of microplastics and their adsorbed substances by soil animals (the springtail, Folsomia candida) and the effect of the transfer on the decomposition of soil organic matter through a standardized cotton strip assay. The results showed that springtails had a strong ability to transfer microplastics into the soil. The adsorbed nutrient (nitrogen; N), pollutant (cadmium; Cd), and green fluorescent Escherichia coli (GFP-E. coli) were also transferred with the microplastics. In addition, cotton strip decomposition was accelerated when the microplastics adsorbed N, but the adsorption of Cd decreased decomposition. These ecological effects were particularly strong for small microplastics. Microplastic transfer regulated soil bacterial communities, promoting the growth of Ascomycota fungi and inhibiting that of Basidiomycota, leading to cotton strip decomposition. Thus, microplastic pollution may occur at one site, but microplastics can be transferred anywhere in terrestrial ecosystems by soil animals and adsorb other substances, including nutrients and pollutants, that affect ecosystem function. Therefore, more studies on the migration behaviour of microplastics are necessary.

Cotton strip assay detects soil microbial degradation differences among crop rotation and tillage experiments on Vertisols

The cotton strip assay (CSA) is a simple and inexpensive method of evaluating management effects on soil microbial decomposition. The average loss of tensile strength of cotton strips buried 3 to 35 days in soils from two long-term tillage and crop-rotation experiments was of the order: cotton-wheat rotation > minimum-tillage cotton monoculture > maximum-tillage cotton monoculture. The study suggests CSA can be an effective indicator to delineate microbial activity, soil organic carbon or crop biomass as influenced by agricultural practices in cotton fields.

Organic-matter decomposition in urban stream and pond habitats

Organic-matter decomposition is a key ecosystem process in freshwater ecosystems as it influences food web dynamics, represents a considerable flux in the global carbon cycle and can provide a useful measure of the ‘health’ of freshwater habitats. While organic-matter decomposition has been well studied among lotic ecosystems, research from small standing waterbodies such as ponds is largely missing, and decomposition studies are usually conducted on a single freshwater habitat type. However, there is a need to consider ecosystem processes across multiple freshwater habitats and connected ecosystems to better characterise ecosystem functioning at the landscape-scale, given the interdependence of landscape elements. This study provides a comparative analysis of organic-matter decomposition using a standardised field assay (cotton-strip assay) in the water column, riparian zone and land zone of urban pond and stream habitats. The average daily tensile-strength loss of the cotton strips (a process that corresponds to the catabolism of cellulose by microbes) was significantly higher in the aquatic habitats than riparian and land zones when all sites were considered, and when stream and pond sites were considered separately. Furthermore, the average decomposition rate was significantly higher within the water column in river habitats compared to pond habitats, although no difference was observed among riparian and land zones. Woody debris had a negative unimodal association with average per day tensile strength loss within streams, and a positive unimodal association within pond sites. Both nitrate and shading had positive unimodal associations with average per day tensile strength loss within stream sites. Among pond habitat, urban land coverage within 250m of each site was identified to have a negative association with average per day tensile strength loss. Here we demonstrated that urban freshwater habitats have heterogeneous organic matter decomposition rates, and that the responses can be complex. Understanding key ecosystem processes at a multihabitat scale will ensure the effective inclusion of ecosystem process in freshwater assessment and conservation protocols and improve the health and resilience of urban freshwater ecosystems.

Organic Matter Decomposition in River Ecosystems: Microbial Interactions Influenced by Total Nitrogen and Temperature in River Water.

Microbes contribute to the organic matter decomposition (OMD) in river ecosystems. This study considers two aspects of OMD in river ecosystems which have not been examined in scientific studies previously, and these are the microbial interactions in OMD and the influence of environmental factors on microbial interactions. Cotton strip (CS), as a substitute for organic matter, was introduced to Luanhe River Basin in China. The results of CS assay, microbial sequencing, and redundancy analysis (RDA) showed that CS selectively enriched bacterial and fungal groups related to cellulose decomposition, achieving cotton strip decomposition (CSD). Bacterial phylum Proteobacteria and fungal phyla Rozellomycota and Ascomycota were the dominant groups associated with CSD. Network analysis and Mantel test results indicated that bacteria and fungi on CS cooperatively formed an interaction network to achieve the CSD. In the network, modules 2 and 4 were significantly positively associated with CSD, which were considered as the key modules in this study. The key modules were mainly composed of phyla Proteobacteria and Ascomycota, indicating that microbes in key modules were the effective decomposers of CS. Although keystone taxa were not directly associated with CSD, they may regulate the genera in key modules to achieve the CSD, since some keystone taxa were linked with the microbial genera associated with CSD in the key modules. Total nitrogen (TN) and temperature in water were the dominant environmental factors positively influenced CSD. The key modules 2 and 4 were positively influenced by water temperature and TN in water, respectively, and two keystone taxa were positively associated with TN. This profoundly revealed that water temperature and TN influenced the OMD through acting on the keystone taxa and key modules in microbial interactions. The research findings help us to understand the microbial interactions influenced by environmental factors in OMD in river ecosystems.

Impaired cellulose decomposition in a headwater stream receiving subsurface agricultural drainage.

BackgroundAgricultural development of former wetlands has resulted in many headwater streams being sourced by subsurface agricultural drainage systems. Subsurface drainage inputs can significantly influence stream environmental conditions, such as temperature, hydrology, and water chemistry, that drive ecological function. However, ecological assessments of subsurface drainage impacts are rare. We assessed the impact of an agricultural drainage system on cellulose decomposition and benthic respiration using a paired stream study in a headwater branch of Nissouri Creek, in Ontario, Canada. Adjacent first order segments sourced by a spring-fed marsh and a cropped field with subsurface drainage, as well as the adjoining trunk segment, were sampled over a year using the cotton strip assay to measure cellulose decomposition and benthic respiration.ResultsAssessments of cellulose decomposition revealed a one-third reduction in the drainage-sourced segment compared to marsh-sourced segment. Between segment differences in cellulose decomposition were associated with reduced summer temperatures in the drainage-sourced segment. Impacts of stream cooling from the drainage-sourced segment were transmitted downstream as cellulose decomposition was slower than expected throughout the drainage-sourced segment and for several hundred meters down the adjoining trunk segment. Benthic respiration only differed between the drainage- and marsh-sourced segments in spring, when stream temperatures were similar.ConclusionsOur findings suggest there may be a widespread reduction in cellulose decomposition in streams across similar agricultural regions where subsurface drainage is prevalent. However, cooling of streams receiving significant amounts of water inputs from subsurface drainage systems may impart increased resiliency to future climate warming.

Temporal and spatial variation in bacterial communities on uniform substrates in non‐wadeable rivers

AbstractUndertaking environmental assessments on non‐wadeable rivers is challenging due to their size, depth, and water velocity. The cotton strip assay (CSA) is a functional indicator used in assessing the ecological health of non‐wadeable rivers by measuring cellulose decomposition potential. Enhancing knowledge on the microbial communities responsible for decomposition would assist in developing a microbial‐based biotic index that could complement the CSA. The aims of this study were to explore the temporal and spatial variability of bacterial communities on cotton strips, identify environmental drivers of differences, and detect potential indicator taxa. Cotton strips were deployed at 12 sites, spanning a range of water quality and catchment land uses in three separate months. Each site was placed into an ecological health category (EHC) from A (healthy) to D (poor). Metabarcoding (16S rRNA) was used to characterize bacterial communities. There was a significant interaction between month and site and between month and EHC. Higher temperatures and pH were identified as key drivers of differences in bacterial communities in February (summer) and higher levels of ammoniacal nitrogen, nitrate/nitrite nitrogen, and turbidity in August (winter). After removal of amplicon sequence variants (ASVs) in low abundance, 27 taxa indicative of EHCs were identified. ASVs associated with EHC‐A were generally negatively correlated with modified land use and nitrate/nitrite nitrogen. In contrast, ASVs associated with EHC‐D were positively correlated to modified land use and temperature. With further validation, a molecular microbial index could be developed to aid in assessing the health of non‐wadeable rivers.

Monitoring organic-matter decomposition and environmental drivers in restored vernal pools

Vernal pools are small, shallow and ephemeral freshwater wetlands, often located in forests. Despite harboring high levels of biodiversity and being biochemical hotspots, they have been severely degraded by human activities. Restoration of vernal pools has become a priority for resource managers, and monitoring of restoration projects is needed to track the effectiveness of restoration techniques. In this study, we analyzed the ecological functioning of natural and restored vernal pools in the forest of Chinon (France) four years after a restoration project. Specific aims were to: (1) compare organic-matter decomposition rates between natural and restored pools, and (2) evaluate the main drivers of organic-matter decomposition in these two types of pool. In five natural and nine restored vernal pools, a standardized organic-matter decomposition assay (cotton strip) was deployed for up to 57 days. Each pool was characterised in terms of vegetation type, water and soil quality. We found that decomposition rates did not differ between natural and restored pools. The natural pools, however, had the greater stores of total organic carbon (TOC) content, and Sphagnum moss cover. Across both pool types, decomposition rates were positively associated with canopy openness and vascular plant cover, suggesting a possible ‘priming effect’ of primary producers on microbial decomposers. Sphagnum moss cover and some soil variables, such as TOC, were associated with slowed decomposition, highlighting the potential of Sphagnum spp. at influencing microbial activity. We suggest that future studies couple the cotton strip assay with biotic indices to assess the overall functioning of these wetlands.

Negative Feedback by Vegetation on Soil Organic Matter Decomposition in a Coastal Wetland

There has been much debate about the external drivers that affect the decomposition of soil organic matter (SOM). Particularly, the feedback mechanisms between SOM and mineral weathering are poorly understood. We used the cotton strip assay combined with measurements of water table, pore water salinity, and soil properties along a landscape-scale gradient to study these mechanisms. The results revealed that cotton tensile strength loss (CTSL) rates ranged from 2.0% day−1 to 4.6% day−1 and varied significantly among sites and depths. A multiple regression model revealed that the corelation between the CTSL and submersion duration (SD) was positive when the chemical index of alteration (CIA) was ~65% and negative over most of the range of SD when the CIA was ~45%. The results suggest that the hydrological conditions induced by tidal effects endanger the stocks of carbon sequestered in coastal wetland soils. However, sites with CTSL rates as high as 4.0–5.0% day−1 tended to gain more nutrients than sites with lower CTSL rates. The fixation of atmospheric CO2 via plant growth may therefore be stimulated in coastal wetland soils by the recycling of mineral nutrients via enhanced weathering. The result is a negative feedback of the ecotone on SOM decomposition.

Decomposition in flocculent sediments of shallow freshwaters and its sensitivity to warming

Shallow waterbodies are abundant in many landscapes across the globe and are increasingly acknowledged for their role in freshwater C cycling. This study investigated organic-matter decomposition potentials in flocculent organic sediment, a rarely-investigated sediment type commonly found in shallow waters. Further, this study investigated how porewater chemistry and temperature affect decomposition rates within flocculent sediment. We quantified decomposition rates during 3 seasons by deploying a standardized substrate (cotton strips) within and above the flocculent sediment layer in the littoral zones of lakes, shallow through-flow wetlands, and depositional zones on the margins of stream channels of southwestern Michigan, USA. We then compared our results with those reported for other freshwater settings that used the same cotton-strip assay. There was high accumulation of organic matter in the shallow waterbodies, but decomposition rates in flocculent sediments averaged 1.7× greater than rates measured in oxic overlying waters and were generally only eclipsed by temperature-adjusted rates reported in streams, which are typically well-oxygenated, flowing environments. Rates were positively correlated with sediment porewater concentrations of soluble reactive P and dissolved iron and negatively correlated with ammonium. Warmer temperatures also resulted in increased decomposition rates, and the temperature sensitivity results suggest that decomposition rates in flocculent sediments could increase 11 to 52% with a 1 to 4°C increase in water temperatures, a realistic range of increase for this region in the next 100 y if climate change continues at the current pace. Thus, high organic matter inputs, rather than slow decomposition, must lead to the development of flocculent organic sediments. Future warming could therefore increase decomposition rates and tip the balance toward net losses of organic matter.

The cotton-strip assay as an environmental surveillance tool for ecological integrity assessment of rivers affected by WWTP effluents

Environmental impact studies of rivers affected by wastewater treatment plant (WWTP) effluents have been greatly restricted by the difficulties associated with carrying out bioassays in the field and also by the complex interactions between the pollutants contained in the discharges. The cotton-strip assay (CSA) enables study of the organic matter decomposition potential, an important ecosystem process in rivers, by taking all of the factors affecting this process into account. However, the CSA has never been used for assessment of WWTP effluents. In the present study, we selected six fluvial zones affected by discharges from small WWTPs and placed cotton strips at increasing distances from the discharge points in each zone. After 17 days, we evaluated decay of the strips by measuring cotton tensile strength loss (CTSL) and cotton mass loss (CML). We then determined the relationships between these parameters and various physico-chemical and biological properties in the water, as well as the δ15N isotopic signal and metal contents of aquatic mosses transplanted in the same sampling sites and used as biomonitors. Although the WWTPs were similar, some of the discharges stimulated and others inhibited decomposition of the cotton strips. This was probably due to differences in the proportions of various types of pollutants (with trophic or toxic effects) in the discharges. The CSA proved to be a simple, practical and economic bioassay and suitable for evaluating the ecological integrity of fluvial ecosystems.

Hierarchical variation in cellulose decomposition in least-disturbed reference streams: a multi-season study using the cotton strip assay

Context Decomposition of organic matter dictates productivity of headwater streams in forested biomes. However, the hierarchical structure of stream ecosystems entails that research aimed at understanding patterns and drivers of decomposition incorporate multiple spatio-temporal scales.

Combined Effects of Vegetation and Drought on Organic-Matter Decomposition in Vernal Pool Soils

Despite their small size, vernal pools are hotspots for biogeochemical processes and biodiversity. To better understand their functioning, we studied the influence of vegetation (Sphagnum palustre, Molinia caerulea (L.) Moench) on organic-matter (OM) decomposition in soils, during periods of drought. OM decomposition rates were quantified by using a cotton-strip assay and field mesocosms. Decomposition rates were slower in the water-logged soils because hypoxic conditions decreased microbial activity. The vegetation type is also shown here to be related to decomposition rates. Indeed, the combined effect of Molinia caerulea and Sphagnum palustre reduced them compared to the presence of Sphagnum palustre alone or bare soil. We hypothesize that M. caerulea may have negative impacts on the microorganisms through a negative priming effect or allelopathic interactions.

Organic-matter decomposition along a temperature gradient in a forested headwater stream

AbstractWe used a natural temperature gradient in Walker Branch, a spring-fed forested stream in eastern Tennessee, USA, to examine the influence of temperature on organic-matter decomposition. In this stream, upstream sites are warmer than downstream sites in winter and are cooler than downstream sites in summer. We used a cotton-strip assay to examine breakdown of a substrate of uniform quality (95% cellulose) along the temperature gradient monthly for 2 y. We also used litter bags to examine the interactive effects of leaf-litter quality (labile red maple [Acer rubrum] and tulip poplar [Liriodendron tulipifera] and less labile white oak [Quercus alba]), invertebrates, and temperature on breakdown rates along the downstream temperature gradient for 90 d in winter. Cotton-strip tensile loss and leaf-litter breakdown rates were highly variable. Tensile-loss rates probably were driven by a combination of daily and diel temperature, discharge, and streamwater nutrients that varied seasonally and spatially a...

Cotton-strip decomposition rate as a river condition indicator – Diel temperature range and deployment season and length also matter

Decomposition of organic matter, a fundamental ecological process, has been proposed to be used as a functional indicator of stream condition. A recently published protocol for the use of the cotton-strip assay as a standardized measure of decomposition rates provided a basis for the use of decomposition as an indicator. However, some factors that may influence the application of the cotton-strip assay, such as the deployment season, remain largely unexplored. To further establish the technique, we studied temporal and spatial variability in cotton-strip decomposition rates along small upland rivers in SE Australia. We found a consistent longitudinal pattern in decomposition rates throughout the year, in spite of large within-site and site-specific temporal variability. Results from the models of temporal variability in decomposition rates indicate that differences in the duration of incubation might have been a confounding variable. Models of spatial variability in decomposition rates explained 45% and 52% of the variability in decomposition rates across five rivers, with diel temperature range being the most important predictor, accounting for ca. 20% of the variability in decomposition rates. We have shown that additional considerations are needed, if decomposition rates are to be compared across spatial and temporal scales. First, large within-site variability in decomposition rates, found in our and other studies, might prevent comparisons with reference conditions. Second, the length (and therefore the season) of cotton-strip deployment needs to be specified, since the exponential decomposition coefficient appears not to be a constant throughout time. Third, diel temperature range needs to be considered when establishing sampling protocols, since the exponential decay coefficient appears to change non-linearly with changing temperature, and therefore, using only daily mean temperatures does not realistically reflect the effect of temperature. The importance of temperature range also has implications for stream rehabilitation, showing that restoring the temperature regime contributes to the restoration of a fundamental ecosystem process.

A standardized cotton-strip assay for measuring organic-matter decomposition in streams

Assessment of stream ecosystem ‘health’ traditionally uses structural indicators (e.g., invertebrate community composition) but often neglects indicators of ecosystem processes (e.g., decomposition rates), providing an incomplete picture of overall ecosystem condition. Given a lack of standardized process-based indicators, we present a protocol for measuring organic-matter decomposition, represented by the breakdown of cellulose in the form of woven cotton fabric. The material, used more conventionally as artists’ fabric, has been suggested as a replacement for a standard cotton material (Shirley Burial Test Fabric) that had been widely used in decomposition studies for decades but is no longer manufactured. In field trials, we incubated cotton strips made of artists’ fabric in 49 streams in the Midwest (USA), northern Michigan (USA), and in New Zealand to: (1) test the assay under field conditions, (2) provide an initial population of data to which future studies can be compared, and (3) assess some environmental conditions that might influence cotton-strip decay. Decomposition of the strips, as loss of tensile strength, differed among regions and, in some cases, among streams within regions, suggesting that the assay is sensitive to differences in environmental conditions at regional and watershed scales. Mean rates (and standard deviation) of tensile-strength loss across streams of tensile-strength loss were 2.3%/d (0.4), 1.8%/d (0.7), and 1.5%/d (1.0) for the midwestern, Michigan, and New Zealand streams, and 1.7%/d (0.8) overall. Principal components analysis indicated that stream water ammonium and soluble reactive phosphorus explained a small but significant amount of variation (R2=0.12) in tensile-strength loss among streams. Rates of respiration of cotton strips incubated in Michigan streams were positively related to tensile-strength loss (R2=0.70). When streams were classified by substrate size, cotton-strip tensile strength (but not respiration) differed among substrate size classes. We conclude that a cotton-strip assay based on the artists’ fabric holds promise for replacing the assay based on the Shirley material, and as a process-based indicator for assessing the condition of stream ecosystems.

Forest clearance increases metabolism and organic matter processes in small headwater streams

Small headwater streams are abundant components of the riverine landscape where critical biochemical processes occur that provide clean water, energy, and nutrients to downstream reaches. Disturbance to these systems as a result of human land use has the potential to affect downstream health. Rates of metabolism and organic matter processing were measured in 22 small forested headwater streams in 2 regions of Tasmania, Australia, to evaluate the effects of forestry disturbance. Twelve of these streams had been subjected to recent clearfell-burn-and-sow (CBS) harvest. Benthic metabolism was measured in small in situ chambers (production ranged from <0.001 to 21.845 mg C m−2 h−1 and respiration from <0.001 to 4.976 mg C m−2 h−1), whole-system metabolism was estimated based on relative habitat abundance (gross primary production ranged from <0.001 to 0.297 g C m−2 d−1 and daily respiration from 0.003 to 0.072 g C m−2 d−1). Algal growth potential was measured on nutrient diffusing pots (chlorophyll a ranged from <1.0 to 40.1 mg/m2), and cellulose decomposition potential was assessed with a cotton-strip assay (cotton tensile strength loss ranged from 17.8% to 38.3% in 28 d). Sometimes an increase in the variability of response is a consequence of disturbance, but in our study, the difference between forested streams and clearcut streams was a significant increase in the mean values of all functional variables. The degree of response depended on the underlying geology (broad-scale spatial variability) of the streams. Current management practices for small headwater streams in Tasmania do not protect instream processes from forestry disturbance in the short-term (i.e., 2–5 y), and we suggest that an investigation of long-term response is warranted.

Mountain lakes increase organic matter decomposition rates in streams

Lakes can play a large role in structuring the chemical and physical templates of streams, yet they often are overlooked when stream function is evaluated. We examined how lakes within stream networks affect organic matter decomposition. We used a cotton-strip assay to evaluate cellulose decomposition potential (CDP) as loss of cotton-strip tensile strength in streams upstream and downstream of 4 mountain lakes in a lake district in the Sawtooth Mountains, Idaho. In addition, we used this assay to determine decomposition potentials along a longitudinal gradient in 1 stream–lake network. Decomposition coefficients (k) were 43% greater in lake-outflow streams than lake-inflow streams. Temperature explained 65% of the variability in decomposition rates across lake inflows and outflows, and decomposition rates in inflow streams were highly correlated with mean daily temperature (r = 0.99). Conversely, decomposition rates in outflow stream were strongly correlated with total N/total P ratios (TN/TP; r = 0.94). When temperature ranges were small, as was observed across 4 lake outflows and along a longitudinal gradient, decomposition rates appeared to be driven by differences in nutrient availability, mainly TP and, to a lesser extent, TN. Together, these results demonstrate that although temperature is a primary driver of decomposition, when temperature is similar across locations, nutrient availability can drive decomposition rates. Our results indicate that lakes within fluvial networks can modify stream function by altering both temperature and nutrient availability.

Is cotton-strip tensile strength a surrogate for microbial activity in groundwater?

The cotton strip assay uses the loss of tensile strength of cotton strips as a measure of microbial cellulolytic activity. Its suitability for measuring general microbial activity in groundwater was tested by examining the relationship of tensile strength, abundance of cellulolytic organisms and general microbial activity on cotton strips deployed in bores. The hypothesis was that the strength of cotton strips would decline with increasing abundance and activity of cellulolytic organisms, and as cellulolysis makes resources available to other microbial groups, cotton strength loss should also be related to increased overall microbial activity. The correlation between the abundance of cellulolytic organisms and cotton strength was not significant. Two main factors influenced this relationship: (i) effectiveness of the media in detecting cellulolytic moulds and (ii) inter-community interactions. After accounting for the presence of moulds through partial correlation, the relationship between tensile strength and abundance of cellulolytic organisms was stronger and significant. Both cotton strength and abundance of cellulolytic organisms correlated significantly with general microbial activity. These results support the use of the cotton strip assay, and cotton tensile strength as a surrogate for microbial activity in groundwater.

Cotton strips as a leaf surrogate to measure decomposition in river floodplain habitats

AbstractLeaf-litter assays have advanced understanding of decomposition processes in both terrestrial and aquatic ecosystems. Some shortcomings inherent in the technique may be overcome through use of a cotton-strip assay. Key assumptions for using cotton strips as proxies for natural leaves are: 1) decomposition rates of the 2 materials are related, and 2) the materials decay in a similar way when exposed to the same environmental conditions. These assumptions were tested by comparing cotton-strip decomposition (loss of tensile strength and mass) and leaf decomposition (mass loss) across different floodplain habitats of the Tagliamento River (northeastern Italy). Patterns of loss of cotton-strip tensile strength and leaf mass were broadly comparable across river channels, ponds, and terrestrial sites. Differences between river channels and ponds were greater for loss of cotton-strip tensile strength than leaf mass, indicating that, in some situations, loss of cotton-strip tensile strength may be more sen...