Organic Matter Budgets for Streams: A Synthesis

Large-Scale Trends for Stream Benthic Respiration

Organic material transport in the New River, Virginia, was investigated over a 12 month period. Collections were made using drift nets and grab water samples from bridges at two sites about 210 km apart. About midway between the two sampling sites is a 1920 ha impoundment used for flood control and power generation. Dissolved organic matter (DOM) ranged 1–50 mg l−1 at Site 1, upstream from the impoundment, and 11–19 mg l−1 at Site 2 and was the most abundant form of organic matter at both sites during most periods of the year. Fine particulate organic matter (FPOM) ranged 1–45 mg l−1 at Site 1 and 1–9 mg l−1 at Site 2. Concentration of coarse particulate organic matter (CPOM) ranged 0.1–0.7 mg l−1 at Site 1 and 0.1–0.2 mg l−1 at Site 2. On an annual basis, the organic matter loads at Site 1 and Site 2 were computed to be 67 000 and 76 800 T y−1, respectively, suggesting that the impoundment trapped and processed POM, and that municipal and industrial treatment facilities between the study sites supplemented DOM in the river.

Summary1. River food webs rely on two major food sources: autochthonous primary production within the river and allochthonous organic matter transferred to the river. We characterised the consumer communities and assessed the food sources of dominant consumers along a subtropical mountainous river (the Lanyang River of north‐eastern Taiwan) at the catchment scale from the headwater to the estuary using natural abundances of stable carbon and nitrogen isotopes.2. The downstream transport of fine particulate organic matter (FPOM) was two orders of magnitude greater than that of coarse particulate organic matter (CPOM). Transport of both materials increased from the headwater and reached a maximum in the midstream reach. CPOM composition exhibited a gradual shift from leaves and branches in the headwater, an area characterised by high canopy cover, to algae in the midstream reaches and marsh plants in the downstream reaches.3. Consumer communities can be classified into two regional categories: the upland category in the headwater and upstream and midstream reaches and the lowland category comprised of samples from the downstream reach and estuary. The upland category revealed a clear and gradual seasonal shift in community composition, but a seasonal shift was not apparent for the lowland category. Nutrient concentrations and water temperature were the main factors explaining longitudinal and seasonal variations.4. The use of sources of organic matter by dominant consumers along the Lanyang River was primarily determined by their availability. Riparian C3 plants were the major food sources in the headwater, upstream reach and estuary, but the contribution of periphyton increased in the upper midstream reach where the river flows through an agricultural area. In the lower midstream and downstream reaches, the contribution of riparian C4 plants became dominant.5. The trophic transfer of organic materials in the Lanyang River may be influenced by the fast current velocity and by sewage nutrient loading in the river, both of which have important implications for predicting how the functioning of subtropical river food webs will respond to human‐related changes in land use.

Summary1. The magnitude and spatial scales of human effects on stream habitats need to be correctly measured to achieve sound ecosystem management. We investigated whether the biogeochemical properties of fine particulate organic matter (FPOM) might be indicative of reach‐scale vs. catchment‐scale effects on forested stream ecosystems.2. Along each of three forested streams, we established 4–5 sampling stations at 0·6–2·0‐km intervals, which represent a range of local riparian forest conditions (e.g. vegetation types and forestry practices). At each station, rock biofilm (considered as a representative of stream‐origin POM), FPOM in sediment (FPOMS) and suspended in water (FPOMW) and three species of benthic macroinvertebrates were collected during a summer low‐flow period.3. Measures of δ13C, C:N and chlorophyll a:C for FPOMW, FPOMS and biofilm were longitudinally heterogeneous, reflecting the reach‐scale, local environment. δ13C, C:N and chlorophyll a:C of FPOMS were significantly related to irradiance and streambed coarse particulate organic matter (CPOM) abundance, suggesting that the relative contribution of in‐stream primary production and CPOM breakdown are dominant controls of FPOM properties.4. In redundancy analysis, variations in FPOM properties were principally explained by local environmental factors correlated with stream size and/or longitudinal position of the sampling stations (irradiance, streambed CPOM, stream gradient, discharge, riparian vegetation). No significant effect of riparian forestry activities (logged, riparian reserve or no harvest in the past 75 years) was found on FPOM properties.5. Resource use by primary consumers was species dependent. δ13C of larval Lepidostoma roafi depended on the relative abundance of stream‐origin POM in pools of stored FPOM. Selective intake/assimilation of stream‐origin POM by this species was probably enhanced when stream‐origin POM was abundant. δ13C of larval Despaxia augusta or larval Paraleptophlebia spp. were not related to FPOMSδ13C, suggesting no linkage with FPOM composition.6. Synthesis and applications. The tight linkages between biogeochemical properties of FPOM, resource use by primary consumers, and reach‐scale environment indicate that local effects were greater than signals transmitted from upstream in this study. The use of in‐stream FPOM properties can help managers to measure reach‐scale effects of environmental changes on forested stream habitats.

Traditional sampling methods for dissolved organic matter (DOM) in streams limit opportunities for long-term studies due to time and cost constraints. Passive DOM samplers were constructed following a design proposed previously which utilizes diethylaminoethyl (DEAE) cellulose as a sampling medium, and they were deployed throughout a temperate stream network in Indiana. Two deployments of the passive samplers were conducted, during which grab samples were frequently collected for comparison. Differences in DOM quality between sites and sampling methods were assessed using several common optical analyses. The analyses revealed significant differences in optical properties between sampling methods, with the passive samplers preferentially collecting terrestrial, humic-like DOM. We assert that the differences in DOM composition from each sampling method were caused by preferential binding of complex humic compounds to the DEAE cellulose in the passive samplers. Nonetheless, the passive samplers may provide a cost-effective, integrated sample of DOM in situations where the bulk DOM pool is composed mainly of terrestrial, humic-like compounds.

Contrasting reports have been given on the relationships between soil texture, mineralogy and particulate organic matter (POM). The objective of this study was to determine the effects of soil texture and mineralogy on aggregate POM in several ecotopes in the Eastern Cape province of South Africa. Soil from the surface 0–20 cm was collected from 14 ecotopes. Particulate organic matter was fractionated into litter POM, coarse POM and fine POM. Isolation of the POM fraction was done by dispersing the soil in 5 g l-1 sodium hexametaphosphate and passing the dispersed soil samples through a 0.053 mm sieve. Both total soil organic matter (SOM) and the POM in each fraction were determined using the weight loss on ignition procedure. Most ecotopes were either sandy loam or sandy clay loam and primary minerals especially quartz dominated the soil mineralogy. The clay content was significantly related to the total SOM (r = 0.78), hematite (r = 0.83) and quartz (r = -0.74). The results suggest that in soils that are dominated by primary minerals such as quartz, the clay content, rather than the clay plus silt content, is a better indicator of fine POM and total SOM.

Dissolved organic matter (DOM), produced through leaching from particulate organic matter (POM), is an essential component of the carbon cycle in streams. The present study investigated the instream DOM release from POM, varying in size and chemical quality. We produced large and medium sized fine particulate organic matter (L-FPOM, 250–500 μm; M-FPOM, 100–250 μm) of defined quality by feeding five types of coarse particulate organic matter (CPOM) to shredding amphipods (Gammarus spp.). Microscopic observations showed that L-FPOM and M-FPOM mainly consisted of the fecal pellets of amphipods, and incompletely eaten plant fragments, respectively. DOM release experiments were conducted by exposing CPOM and M- and L-FPOM fractions in natural stream water over a two week period. For CPOM, the release of dissolved organic carbon (DOC) by leaching was highest during the first 6 h (3.64–23.9 mg C g C−1 h−1) and decreased rapidly afterwards. For M- and L-FPOM, the DOC release remained low during the entire study period (range: 0.008–0.15 mg C g C−1 h−1). Two-way ANOVA revealed that the DOC release rate significantly differed with POM source and size fraction, both at day 1 and after a week of exposure. Multiple regression analyses revealed a significant correlation of elemental contents and lignin content to DOC release rate after a week of exposure. Overall, the results indicated that DOC release rate of FPOM, on a carbon basis, is comparable to that of CPOM after leaching, while size and source of POM significantly affect DOC release rate.

Retention of coarse particulate organic matter (CPOM) is essential to the efficient use of organic matter in streams supported by allochthonous inputs. To measure retention and to study factors affecting retention, we conducted both long-term and short-term experiments using small dowels as indices of stick retention and pieces of paper as indices of leaf retention. These experiments were done in streams at Coweeta Hydrologic Laboratory. In general, we found that both types of CPOM were efficiently retained in all streams. Factors that affected CPOM transport and retention were storms, stream size, stream depth, and the abundance of retention structures in the streams. After initial transport, woody CPOM was transported only during storms. Retention was greater in smaller streams and in shallower stream sites. Rocks, boulders, and woody debris were the most important retention structures. In the stream draining a logged catchment, lower CPOM retention was associated with lower abundance of woody debris dams.

Both ?14C, ?13C for the particulate organic matter (POM) and 3-Dimensional Excitation and Emission Matrix spectroscopy (3D-EEM) for the dissolved organic matter (DOM) were used to study transport behavior from land to ocean in Hokkaido, Japan. The ?14C values of the Tokachi POC (particulate organic carbon) show similar variations to Ishikari. However, the variation range of the Tokachi of ?14C is smaller than that of the Ishikari POC. ?13C values for the Ishikari showed larger variation range than those of the Tokachi. The POC during spring snow-melting for the Ishikari and in autumn during heavy rain fall for the Tokachi were distinctive in the correlations of POC, ?14C, and ?13C.There were two different pathways in the correlations of POC content, ?14C, and water discharge for both river systems. The significant pathway during snow-melting found in the Ishikari and at autumn during heavy rain fall for the Tokachi. The Tokachi and the Ishikari River showed similar variations patterns of dissolved organic carbon (DOC) concentrations and relative fluorescence intensity (RFI). The run-off point of DOC and FA-like materials is similar to POC. Therefore, characteristics and export of POC and DOC may be controlled by water discharge in small rivers in sub-arctic zone. The both rivers showed averaged POC flux from 1.43~1.51 ¥ 1010 g/yr, DOC flux of 0.98~2.32 ¥ 1010 g/yr, and fulvic-like materials-carbon (FAC) flux of 0.70~1.22 ¥ 1010 g/yr. The percentages of POC, DOC, and FAC flux in two rivers during snow-melting and heavy rainfall were 78~95% and 25~ 42 %, respectively. The watersheds of the Ishikari and Tokachi are important in transport of POC from land to ocean, especially during snow-melting and heavy rain event. DOI: http://dx.doi.org/10.3329/dujs.v63i1.21768 Dhaka Univ. J. Sci. 63(1): 47-51, 2015 (January)

The role of predator density and plant detritus in determining patterns of insect abundance was tested in an Appalachian stream community (Reeds Creek, Pendleton Co, West Virginia). Insect colonization was followed over a 21-day period in field enclosures containing different densities of sculpins (Cottus bairdi and Cottus girardi). Sculpins caused no significant reductions in prey abundance; however, the combined effect of a guild of vertebrate predators caused a significant depression in the abundance of Chironomidae and the stonefly Leuctra. Since Chironomidae comprised approximately 85% of the total benthic fauna, vertebrate predation had an important role in the overall structure of the invertebrate community.Total insect abundance and diversity were correlated to the presence of plant detritus. However, this relationship was taxon specific, as abundance was highly correlated to detritus for only selected insect taxa. In general, abundance was best correlated with coarse particulate organic matter (CPOM), compared to fine particulate organic matter (FPOM) or total detritus (FPOM+CPOM+Whole leaf organic matter (LVOM)).This experiment illustrates that the influence of various potential structuring mechanisms is highly taxon dependent.

We determined the distribution of hydrophobic organic contaminants (HOCs) to fractions of natural organic matter in a soil contaminated by chlorophenol wood preservatives more than 30 years ago. The concentration of dissolved organic matter (DOM) was enhanced in soil suspensions by raising pH to 6.8-9.1. After 48 h of desorption/equilibration, the DOM fraction was separated from the particulate organic matter (POM) of the soil by filtration. In the next step, DOM was flocculated by Al-nitrate, and free concentrations of HOCs were determined in the aqueous phase. The HOCs associated with DOM and POM were extracted with toluene. No significant differences in gross carbon chemistry were detected between DOM and POM, using X-ray photoelectron spectroscopy (XPS). Normalized to organic C, chlorophenols (CPs) showed a similar degree of partitioning between DOM and POM, whereas the partitioning of polychlorinated diphenyl ethers (PCDEs), polychlorinated dibenzo-p-dioxins, and furans (PCDD/Fs) was highly shifted toward POM. The partitioning to POM, relative to DOM, increased in the order PCDE < PCDF < PCDD, reflecting the hydrophobicity of the compounds.

Tillage has been associated with soil organic matter (SOM) decline. A case study of two adjacent farms was conducted in eastern South Dakota. One farm used no‐till (NT) and the other used chisel tillage (CT). We hypothesized that soil under NT, compared with tillage, would have both greater quantity and greater quality of SOM and that this improved SOM condition would result in increased water stable aggregation (WSA). A rotary sieve was used to sort dry field aggregates into six size groups: &lt;0.4, 0.4 to 0.8, 0.8 to 2.0, 2.0 to 6.0, 6.0 to 19.0, and &gt;19 mm. Water stable aggregation, soil organic C (SOC), N, glomalin, and basidiomycete fungi were measured. Fine particulate soil organic matter (fPOM, 0.5–0.053 mm) and coarse particulate organic matter (2.0–0.5 mm) were isolated by sieving. Quantitative solid‐state 13 C nuclear magnetic resonance was used to determine C type in humic acid, humin, and whole soil. The fPOM/SOM ratio was greatest in &lt;0.4‐mm aggregates and 24% greater in NT than CT. Soil organic C was greatest in 0.8‐ to 2.0‐mm aggregates and 11% greater in NT than CT. Average WSA was 63% greater under NT than under CT. Aggregate wettability was less under NT than CT. Slower water uptake under NT might be attributed to a greater abundance of wax‐type C under NT than under CT. We conclude that NT, compared with CT, resulted in better SOM quality during the course of 10 yr. Improved SOM quality was related to improved WSA.

Biogeochemistry of terrestrial ecosystems is controlled by interactions among factors operating at several spatial and temporal scales. The purpose of this study was to evaluate the relative importance and interaction of relatively static landscape factors and more dynamic factors in a shortgrass steppe landscape. The landscape factors examined were topographic position, and soil texture. The dynamic factors studied were seasonal climate and the localized effects of individual plants on soils. Patterns were evaluated by sampling soil between and under individual Bouteloua gracilis plants in paired upland (erosional) and lowland (depositional) plots at eight locations at the Central Plains Experimental Range (CPER), Colorado. We quantified five organic C and N pools (total, fine and coarse particulate organic matter [POM], mineral-associated organic matter [MAOM], and potentially mineralizable C and N), and we estimated seasonal patterns of in situ N dynamics with three methods (extractable inorganic N, net N mineralization in uncovered cores, and N adsorbed on ion exchange resin [IER] bags). Topographic position and soil texture each explained much of the landscape-scale variation of C and N pools and vegetation structure. Most lowland plots were enriched in silt, clay, C, and N relative to adjacent upland plots, and topographic position affected most pools significantly. Most vegetation and biogeochemical variables were strongly correlated with soil sand content. Across the range of sand content encountered (40–83%), the fraction of area in bare soil openings >5 cm across increased sevenfold, and most C and N fractions increased by 2–4.5 times. Plant-induced, microscale heterogeneity of soil C and N was comparable in magnitude to landscape-scale heterogeneity for pools with more rapid turnover (POM and mineralizable C and N), but presence or absence of plants did not affect more stable, mineral-associated organic matter. Plant-induced heterogeneity was significant in all locations, but its importance likely decreases with decreasing sand content as cover becomes more continuous, particularly in lowlands. Total extractable inorganic N and nitrate, N adsorbed on resin bags, and the proportion of mineralized N that was nitrified during incubations increased with increasing soil water content or precipitation, but net N mineralization did not vary systematically with precipitation. Inorganic N availability was greatest during relatively moist spring periods, and these were the only times when indices of in situ N availability followed the spatial patterns expected from laboratory assays of C and N pool distribution. The relatively weak spatial patterns for N dynamics contrast with the substantial landscape and individual-plant scale variation in C and N pools. Landscape patterns of N mineralization and availability may be tied to N pools, such as POM N, that are not strongly related to topography or texture. Particulate organic matter appears to be especially important to N retention and availability on sandy soils, which typify most sites at the CPER; the proportion of total N residing in POM was high and POM C:N ratios were low in sandy upland soils. We suggest that soil texture is a key proximal control over biogeochemical processes and is largely responsible for observed landscape-scale patterns, including topographic differences. Models that integrate effects of texture and topography have the potential to link landscape biogeochemical patterns to short-term processes that directly influence SOM dynamics and to long-term geomorphic processes that influence soil distribution, including eolian redistribution of soil materials, which is important in many dry regions.

Most streams receive substantial inputs of allochthonous organic material in the form of leaves and twigs (CPOM , coarse particulate organic matter). Mechanical and biological processing converts this into fine particulate organic matter (FPOM). Other sources of particles include flocculated dissolved matter and soil particles. Fungi are known to play a role in the CPOM conversion process, but the taxonomic affiliations of these fungi remain poorly studied. The present study seeks to shed light on the composition of fungal communities on FPOM and CPOM as assessed in a natural stream in Nova Scotia, Canada. Maple leaves were exposed in a stream for four weeks and their fungal community evaluated through pyrosequencing. Over the same period, four FPOM size fractions were collected by filtration and assessed. Particles had much lower ergosterol contents than leaves, suggesting major differences in the extent of fungal colonization. Pyrosequencing documented a total of 821 fungal operational taxonomic units (OTU), of which 726 were exclusive to particles and 47 to leaf samples. Most fungal phyla were represented, including yeast lineages (e.g., Taphrinaceae and Saccharomycotina), Basidiomycota, Chytridiomycota and Cryptomycota, but several classes of Pezizomycontina (Ascomycota) dominated. Cluster dendrograms clearly separated fungal communities from leaves and from particles.Characterizing fungal communities may shed some light on the processing pathways of fine particles in streams and broadens our view of the phylogenetic composition of fungi in freshwater ecosystems.

Towards a budget of leaf litter decomposition in a first-order woodland stream