Contrasting nutrient exports from a forested and an agricultural catchment in south-eastern Australia

Dissolved organic carbon (DOC) and total and inorganic nitrogen and phosphorus concentrations were determined over 3 years in headwater streams draining two adjacent catchments. The catchments are currently under different land use; pasture/grazing vs plantation forestry. The objectives of the work were to quantify C and nutrient export from these landuses and elucidate the factors regulating export. In both catchments, stream water dissolved inorganic nutrient concentrations exhibited strong seasonal variations. Concentrations were highest during runoff events in late summer and autumn and rapidly declined as discharge increased during winter and spring. The annual variation of stream water N and P concentrations indicated that these nutrients accumulated in the catchments during dry summer periods and were flushed to the streams during autumn storm events. By contrast, stream water DOC concentrations did not exhibit seasonal variation. Higher DOC and NO₃ ⁻ concentrations were observed in the stream of the forest catchment, reflecting greater input and subsequent breakdown of leaf-litter in the forest catchment. Annual export of DOC was lower from the forested catchment due to the reduced discharge from this catchment. In contrast however, annual export of nitrate was higher from the forest catchment suggesting that there was an additional NO₃ ⁻ source or reduction of a NO₃ ⁻ sink. We hypothesize that the denitrification capacity of the forested catchment has been significantly reduced as a consequence of increased evapotranspiration and subsequent decrease in streamflow and associated reduction in the near stream saturated area.     

Catchment morphometric characteristics,land use and water chemistry in Pampean streams: a regional approach

The Pampean region covers a large surface in central Argentina, but despite the extensive agricultural activities and the high nutrient levels recorded in streams of the region, few authors have analysed the influence of land use on water quality. Here, we evaluated the relationships among catchment attributes (size, morphometry and land cover) and water chemistry in 23 Pampean streams in different seasons (autumn, spring and summer) and at three spatial scales: whole catchment and two scales of riparian buffers (200 and 500 m adjacent to both stream margins). Chloride concentration was positively related to catchment area and negatively related to drainage density. Nitrate level was strongly associated to cropland, but soluble phosphorus concentration showed no relationships with any type of land cover. Land cover at the buffer scale seemed to be more influential than land cover at the whole catchment for nitrogen concentration. The main impact of cropland was the increase of nitrate concentration, while cattle breeding was negatively associated to photosynthetically active radiation (PAR) in autumn and summer and to dissolved oxygen concentration in spring. Our results highlighted the importance of local land use and riparian conservation on streamwater quality.     

Nitrogen retention in the riparian zone of catchments underlain by discontinuous permafrost

1. Riparian zones function as important ecotones that reduce nitrate concentration in groundwater and inputs into streams. In the boreal forest of interior Alaska, permafrost confines subsurface flow through the riparian zone to shallow organic horizons, where plant uptake of nitrate and denitrification are typically high. 2. In this study, riparian zone nitrogen retention was examined in a high permafrost catchment (approximately 53% of land area underlain by permafrost) and a low permafrost catchment (approximately 3%). To estimate the contribution of the riparian zone to catchment nitrogen retention, we analysed groundwater chemistry using an end‐member mixing model. 3. Stream nitrate concentration was over twofold greater in the low permafrost catchment than the high permafrost catchment. Riparian groundwater was not significantly different between catchments, averaging 13 μm overall. Nitrogen retention, measured using the end‐member mixing model, averaged 0.75 and 0.22 mmol N m^?2 day^?1 in low and high permafrost catchments, respectively, over the summer. The retention rate of nitrogen in the riparian zone was 10–15% of the export in stream flow. 4. Our results indicate that the riparian zone functions as an important sink for groundwater nitrate and dissolved organic carbon (DOC). However, differences in stream nitrate and DOC concentrations between catchments cannot be explained by solute inputs from riparian groundwater to the stream and differences between streams are probably attributable to deeper groundwater inputs or flows from springs that bypass the riparian zone.     

Effects of hydrogeomorphic region, catchment storage and mature forest on baseflow and snowmelt stream water quality in second-order Lake Superior Basin tributaries

1. In this study we predict stream sensitivity to non‐point source pollution based on the non‐linear responses of hydrological regimes and associated loadings of non‐point source pollutants to catchment properties. We assessed two hydrologically based thresholds of impairment, one for catchment storage (5–10%) and one for mature forest (<50% versus >60% of catchment in mature forest cover) across two different hydrogeomorphic regions within the Northern Lakes and Forest (NLF) ecoregion: the North Shore [predominantly within the North Shore Highlands Ecological Unit] and the South Shore (predominantly within the Lake Superior Clay Plain Ecological Unit). Water quality samples were collected and analysed during peak snowmelt and baseflow conditions from 24 second‐order streams grouped as follows: three in each region × catchment storage × mature forest class. 2. Water quality was affected by a combination of regional influences, catchment storage and mature forest. Regional differences were significant for suspended solids, phosphorus, nitrogen: phosphorus ratios, dissolved organic carbon (DOC) and alkalinity. Catchment storage was significantly correlated with dissolved silica during the early to mid‐growing season, and with DOC, specific conductance and alkalinity during all seasons. Total nitrogen and dissolved nitrogen were consistently less in low mature forest than in high mature forest catchments. Catchment storage interacted with the influence of mature forest for only two metrics: colour and the soluble inorganic nitrogen : phosphorus ratio. 3. Significant interaction terms (region by mature forest or region by storage) suggest differences in regional sensitivity for conductance, alkalinity, total organic carbon, and colour, as well as possible shifts in thresholds of impact across region or mature forest class. 4. Use of the NLF Ecoregion alone as a basis for setting regional water quality criteria would lead to the misinterpretation of reference condition and assessment of condition. There were pronounced differences in background water quality between the North and South Shore streams, particularly for parameters related to differences in soil parent material and glacial history. A stratified random sampling design for baseflow and snowmelt stream water quality based on both hydrogeomorphic region and catchment attributes improves assessments of both reference condition and differences in regional sensitivity.     

Catchment and reach-scale properties as indicators of macroinvertebrate species traits

1. We used catchment and reach-scale physical properties to predict the occurrence of specific species life history and behaviour traits of aquatic insects across fifty-eight catchments in a mixed land use basin. Catchment-scale attributes were derived using a geographical information system (GIS). Logistic regression techniques were used to model the relationships.
2. The reach-scale properties were highly predictive of species traits. Fourteen of the fifteen traits had significant models with concordance values greater than 68%. Cross-sectional area at bank full discharge, % shallow, slow-water habitats, and % fines were the most important variables.
3. Life history and behavioural attributes were best related to reach-scale physical features. This suggests that species traits exhibit strong relationships to local environmental conditions.
4. Catchment-scale variables had fewer significant models with species traits (four of fifteen), however these variables may have direct or indirect influence on reach-scale properties.
5. Catchment features, in particular surficial geology, influence macroinvertebrate assemblages through their control over channel morphology and hydrologic patterns.
6. The effects of land use were masked by geology (i.e. lacustrine clay geology and rowcrop agriculture were correlated), lack of detail in land use data and the aggregation of the species data.
7. These models reflect the coupling of local environmental conditions and the set of adaptations among the local taxa. These observations underscore the idea that habitat plays a major role in organizing stream assemblages.
8. Using these approaches, predictions can be made about the ability of various taxonomic groupings to track environmental change through time, or for projecting the impact of alternative land management scenarios. Identifying fundamental life history and other traits can improve the selection and evaluation of such indicators.     

Catchment and reach-scale properties as indicators of macroinvertebrate species traits

1. We used catchment and reach-scale physical properties to predict the occurrence of specific species life history and behaviour traits of aquatic insects across fifty-eight catchments in a mixed land use basin. Catchment-scale attributes were derived using a geographical information system (GIS). Logistic regression techniques were used to model the relationships.
2. The reach-scale properties were highly predictive of species traits. Fourteen of the fifteen traits had significant models with concordance values greater than 68%. Cross-sectional area at bank full discharge, % shallow, slow-water habitats, and % fines were the most important variables.
3. Life history and behavioural attributes were best related to reach-scale physical features. This suggests that species traits exhibit strong relationships to local environmental conditions.
4. Catchment-scale variables had fewer significant models with species traits (four of fifteen), however these variables may have direct or indirect influence on reach-scale properties.
5. Catchment features, in particular surficial geology, influence macroinvertebrate assemblages through their control over channel morphology and hydrologic patterns.
6. The effects of land use were masked by geology (i.e. lacustrine clay geology and rowcrop agriculture were correlated), lack of detail in land use data and the aggregation of the species data.
7. These models reflect the coupling of local environmental conditions and the set of adaptations among the local taxa. These observations underscore the idea that habitat plays a major role in organizing stream assemblages.
8. Using these approaches, predictions can be made about the ability of various taxonomic groupings to track environmental change through time, or for projecting the impact of alternative land management scenarios. Identifying fundamental life history and other traits can improve the selection and evaluation of such indicators.     

Riverine invertebrate assemblages are degraded more by catchment urbanisation than by riparian deforestation

1. Restoration of riparian forests has been promoted as a means of mitigating urban impacts on stream ecosystems. However, conventional urban stormwater drainage may diminish the beneficial effect of riparian forests.
2. The relative effects of riparian deforestation and catchment urbanisation on stream ecosystems have rarely been discriminated because urban land use and riparian degradation usually covary. However, land use at three scales (channel canopy cover along a 100-m site, riparian forest cover within 200 m of the channel for 1 km upstream, and catchment imperviousness) covaried only weakly along the lowland Yarra River, Victoria, Australia.
3. We tested the extent to which each land use measure explained macroinvertebrate assemblage composition on woody debris and in the sediments of pools or runs in the mainstem Yarra River in autumn and spring 1998.
4. Assemblage composition in both habitats and in both seasons was most strongly correlated with proportion of catchment covered by impervious surfaces. Sites with higher imperviousness had fewer sensitive taxa (those having a strong positive influence on indicators of biological integrity) and more taxa typical of degraded urban streams. Sensitive taxa rarely occurred in sites with >4% total imperviousness. However, within sites of similar imperviousness, those with more riparian forest cover had more dipteran taxa. Channel canopy cover did not explain assemblage composition strongly.
5. Riparian forest cover may influence richness of some macroinvertebrate taxa, but catchment urbanisation probably has a stronger effect on sensitive taxa. In catchments with even a small amount of conventionally drained urban land, riparian revegetation is unlikely to have an effect on indicators of stream biological integrity. Reducing the impacts of catchment urbanisation through dispersed, low-impact drainage schemes is likely to be more effective.     

The Influence of Landscape Position and Catchment Characteristics on Aquatic Biogeochemistry in High-Elevation Lake-Chains

To examine the influence of landscape characteristics and landscape position on aquatic biogeochemistry, we sampled a total of 76 lakes within 14 different lake-chains spanning the latitudinal extent of the high-elevation Sierra Nevada (California). We measured water chemistry, dissolved organic matter (DOM), nutrients, and biotic variables in study catchments that encompassed representative ranges of area (3–22 km²), elevation (2,200–3,700 m.a.s.l), elevation change (50–700 m), and average slope (13°–26°). Hierarchical models were used to account for variability in biogeochemistry because they explicitly maintain the framework of lakes within individual lake-chains while accounting for variation among lake-chains. Unconditional means models, where lake-chain was a random effect, revealed significant differences among lake-chains for nearly all biogeochemical variables. Models explained 42–95% of this variability, with the majority of the variation (70%) explained by the among lake-chain component. To explore the amount of additional variation explained by lake landscape position, we added lake network number (LNN) to models. LNN explained a significant amount of additional variation (7% average) in 8 of 23 biogeochemical parameters. However, it explained more variability within individual lake-chains (75%), where among lake-chain differences did not obscure patterns. Patterns of increase with LNN were found for dissolved organic carbon and nitrogen, fluorescence of DOM, alkalinity, and bacterioplankton abundance, whereas nitrate and nitrogen to phosphorus nutrient ratios decreased. LNN explained variation because it served as a proxy for underlying catchment characteristics that changed consistently along downstream flow paths. To characterize the amount of variation explained by catchment characteristics alone, we fit a third model that included lake-chain as a random effect and landscape or lake morphometry attributes as fixed effects. Catchment characteristics explained about as much additional variation (6%) as LNN, but for substantially more biogeochemical parameters (18 out of 23). The catchment characteristics most predictive of biogeochemistry were land-cover factors delineating alpine and subalpine zones (elevation, slope, or proportions of rock or shrub cover). In general, catchment characteristics were stronger predictors of biogeochemistry than characteristics of lake morphometry, emphasizing the relative importance of landscape processes in snowmelt-dominated lake ecosystems.     

Patterns and Dynamics of Dissolved Organic Carbon (DOC) in Boreal Streams: The Role of Processes,Connectivity, and Scaling

We bring together three decades of research from a boreal catchment to facilitate an improved mechanistic understanding of surface water dissolved organic carbon (DOC) regulation across multiple scales. The Krycklan Catchment Study encompasses 15 monitored nested research catchments, ranging from 3 to 6900 ha in size, as well as a set of monitored transects of forested and wetland soils. We show that in small homogenous catchments, hydrological functioning provides a first order control on the temporal variability of stream water DOC. In larger, more heterogeneous catchments, stream water DOC dynamics are regulated by the combined effect of hydrological mechanisms and the proportion of major landscape elements, such as wetland and forested areas. As a consequence, streams with heterogeneous catchments undergo a temporal switch in the DOC source. In a typical boreal catchment covered by 10-20% wetlands, DOC originates predominantly from wetland sources during low flow conditions. During high flow, the major source of DOC is from forested areas of the catchment. We demonstrate that by connecting knowledge about DOC sources in the landscape with detailed hydrological process understanding, an improved representation of stream water DOC regulation can be provided. The purpose of this study is to serve as a framework for appreciating the role of regulating mechanisms, connectivity and scaling for understanding the pattern and dynamics of surface water DOC across complex landscapes. The results from this study suggest that the sensitivity of stream water DOC in the boreal landscape ultimately depends on changes within individual landscape elements, the proportion and connectivity of these affected landscape elements, and how these changes are propagated downstream.     

Stream macroinvertebrate response to catchment urbanisation (Georgia, U.S.A.)

SUMMARY 1. The effects of catchment urbanisation on water quality were examined for 30 streams (stratified into 15, 50 and 100 km² ± 25% catchments) in the Etowah River basin, Georgia, U.S.A. We examined relationships between land cover (implying cover and use) in these catchments (e.g. urban, forest and agriculture) and macroinvertebrate assemblage attributes using several previously published indices to summarise macroinvertebrate response. Based on a priori predictions as to mechanisms of biotic impairment under changing land cover, additional measurements were made to assess geomorphology, hydrology and chemistry in each stream. 2. We found strong relationships between catchment land cover and stream biota. Taxon richness and other biotic indices that reflected good water quality were negatively related to urban land cover and positively related to forest land cover. Urban land cover alone explained 29–38% of the variation in some macroinvertebrate indices. Reduced water quality was detectable at c. >15% urban land cover. 3. Urban land cover correlated with a number of geomorphic variables such as stream bed sediment size (–) and total suspended solids (+) as well as a number of water chemistry variables including nitrogen and phosphorus concentrations (+), specific conductance (+) and turbidity (+). Biotic indices were better predicted by these reach scale variables than single, catchment scale land cover variables. Multiple regression models explained 69% of variation in total taxon richness and 78% of the variation in the Invertebrate Community Index (ICI) using phi variability, specific conductance and depth, and riffle phi, specific conductance and phi variability, respectively. 4. Indirect ordination analysis was used to describe assemblage and functional group changes among sites and corroborate which environmental variables were most important in driving differences in macroinvertebrate assemblages. The first axis in a non‐metric multidimensional scaling ordination was highly related to environmental variables (slope, specific conductance, phi variability; adj. R²=0.83) that were also important in our multiple regression models. 5. Catchment urbanisation resulted in less diverse and more tolerant stream macroinvertebrate assemblages via increased sediment transport, reduced stream bed sediment size and increased solutes. The biotic indices that were most sensitive to environmental variation were taxon richness, EPT richness and the ICI. Our results were largely consistent over the range in basin size we tested.     

Drainage ditching at the catchment scale affects water quality and macrophyte occurrence in Swedish lakes

1. We have limited knowledge of the effects of land use in general and of drainage ditching in particular on macrophyte communities in lakes. I quantified catchment land use, including drainage ditching, as well as water quality and the number of macrophyte species in 17 Swedish lakes in summer 2005. 2. Land use within 1 km of the studied lakes was analysed in a geographic information system. The following variables were included: areas of forests, mires, agricultural land and urbanization, length of drainage ditches (classified according to the use of the land they drained), and shortest distance from lake to an urban area. To extract and analyse general trends in the data sets, redundancy analysis was used. 3. Water quality was explained mainly by three land‐use related variables: the lengths of agricultural, forest and mire ditches. The length of agricultural ditches was positively correlated with lake water conductivity, total dissolved solids, Ca, N and total organic carbon (TOC). The lengths of forest and mire ditches were positively correlated with lake water characteristics, especially TOC. 4. The number of species representing different macrophyte life forms was explained by three environmental variables: conductivity, and lengths of forest and agricultural ditches. The numbers of isoetids, nymphaeids, elodeids and total obligate hydrophytes were negatively correlated with length of forest ditches. In contrast, the number of lemnids and helophytes was positively correlated with conductivity and length of agricultural ditches. Furthermore, the number of isoetids was exponentially related (negatively) to lengths of agricultural and forest ditches, indicating a threshold response to drainage ditch length. 5. The results suggest that effects on water quality and macrophyte communities result from drainage ditching in the lake catchments rather than from land use itself. Given the total area of drainage‐ditched land worldwide (millions of ha in Scandinavia alone), drainage ditching should be considered when evaluating environmental impacts on lake water quality and macrophyte occurrence and when determining reference conditions for catchment land use.     

Mechanisms underlying export of N from high-elevation catchments during seasonal transitions

Mechanisms underlying catchment export of nitrogen (N) during seasonal transitions (i.e., winter to spring and summer to autumn) were investigated in high-elevation catchments of the Sierra Nevada using stable isotopes of nitrate and water, intensive monitoring of stream chemistry and detailed catchment N-budgets. We had four objectives: (1) determine the relative contribution of snowpack and soil nitrate to the spring nitrate pulse, (2) look for evidence of biotic control of N losses at the catchment scale, (3) examine dissolved organic nitrogen ( DON) export patterns to gain a better understanding of the biological and hydrological controls on DON loss, and (4) examine the relationship between soil physico-chemical conditions and N export. At the Emerald Lake watershed, nitrogen budgets and isotopic analyses of the spring nitrate pulse indicate that 50 to 70% of the total nitrate exported during snowmelt (ca. April to July) is derived from catchment soils and talus; the remainder is snowpack nitrate. The spring nitrate pulse occurred several weeks after the start of snowmelt and was different from export patterns of less biologically labile compounds such as silica and DON suggesting that: (1) nitrate is produced and released from soils only after intense flushing has occurred and (2) a microbial N-sink is operating in catchment soils during the early stages of snowmelt. DON concentrations varied less than 20–30% during snowmelt, indicating that soil processes tightly controlled DON losses.     

Canonical variables of aquatic bryophyte combinations for predicting water trophic level

Concentrations of soluble reactive phosphorus (SRP), nitrate, and soluble reactive silicon (SRSi) were monitored in 12 streams draining small catchments (<10 km2) in the English Lake District. The catchments varied with respect to underlying geology, soil type and land cover. Average concentrations of SRP were in the range 0.5–11.2 μg P l-1, and estimated loads ranged from 0.01 to 0.14 kg P ha-1 a-1. The higher concentrations and loads were associated with catchments containing improved pasture. Mean streamwater concentrations of nitrate varied from 55 to 660 μg N l-1, while loads were in the range 0.8–9.6 kg N ha-1 a-1; no general dependence on catchment properties was discerned. Concentrations of SRSi were similar in all the streams (0.8–2 mg Si l-1), and annual loads were in the range 10–26 kg Si ha-1 a-1. Loads of all three nutrients were greatest during the winter, because of higher discharges, but in some catchments containing improved pasture, considerable transport of P also took place during the summer. Concentrations of nitrate in streams draining unimproved moorland catchments are approximately twice those reported for samples taken from similar streams in 1973 and 1974, possibly because of increased atmospheric deposition of inorganic nitrogen (ammonium and nitrate). Concentrations of SRP in such streams were similar to those reported for the earlier samples. Comparisons of stream loads of SRP and nitrate with estimated inputs suggest that catchment soils retain substantial amounts of these nutrients. Implications for surface water eutrophication of changes in P retention by soils are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

The influence of catchment characteristics on the seasonality of carbon and nitrogen species concentrations in upland rivers of Northern Scotland

Data from 13 catchments with no arable land in Northern Scotland were used to develop empirical linear regression models of average monthly NO₃ ^? concentrations and average summer and winter concentrations for NH₄ ⁺, dissolved organic N (DON) and dissolved organic carbon (DOC) as a function of catchment characteristics. All catchments displayed a pronounced seasonal NO₃ ^? cycle. Variation in monthly mean NO₃ ^? concentration within and between catchments could be predicted from mean monthly air temperature using separate regression equations for temperatures < and ≥ 5 °C. Soil type, climate and land use influenced NH₄ ⁺ concentrations. In summer, concentrations of NH₄ ⁺ were largest in catchments with extensive areas of brown forest soils, which are less acidic and more base-rich than other upland soils. However, concentrations declined with increasing conifer cover and summer rainfall. In winter, however, % conifer cover had a positive effect, while higher temperature and higher humus iron podzol cover had negative influences. DON concentration decreased with increasing catchment elevation in both summer and winter. Surprisingly, concentrations of DON only displayed a positive relationship with percentage peat cover in the summer. The most important factor controlling DOC concentration was soil type, with a positive relationship being observed between DOC and peat and humus iron podzol coverage. Elevation was also important, but only in the winter when concentrations were negatively correlated with maximum catchment elevation. Overall, multivariate regression equations explained the spatial and seasonal variability in N species concentrations over a range of catchments within Northern Scotland.     

Physico-chemistry and aquatic insects of a glacier-fed and a spring-fed alpine stream

1. Physico-chemical conditions and benthic macroinvertebrates were studied in two adjacent alpine streams in the Tyrolean Alps, Austria, for 2 years, and aquatic insect emergence was recorded for 1 year.
2. In the spring-fed system, maximum discharge and increased concentrations of suspended solids, nitrate and particulate phosphorus occurred during snowmelt in June. In the glacier-fed stream, high discharge and strong diel fluctuations in flow and concentrations of suspended solids created a harsh and unstable environment during summer. Glacial ablation, variation in groundwater inflow, and water inputs from tributaries draining calcareous rocks caused water chemistry to vary both seasonally and longitudinally in glacier-fed Rotmoosache.
3. A total of 126 aquatic or semi-aquatic invertebrate taxa were collected, 94 of which were found in the glacier-fed stream and 120 in the spring-fed stream. Chironomid abundance was 2–8 times and taxa richness 2–3 times lower in the glacier-fed stream than in the spring-fed stream, as was the number of chironomid taxa (72 versus 93 total).
4. These results broadly support the conceptual model by Milner & Petts (1994) concerning glacier-fed stream systems. However, single samples and seasonal means showed relatively high invertebrate abundance and richness, especially during winter, indicating a considerable degree of spatial and temporal variability.
5. We suggest that the seasonal shifts from harsh environmental conditions in summer to less severe conditions in autumn and a rather constant environment in winter are an important factor affecting larval development, life-history patterns and the maintenance of relatively high levels of diversity and productivity in glacier-fed streams.     

The rivers of North East Scotland: physicochemical characteristics

Multivariate analysis of spatial variation in 15 physicochemical characteristics grouped the seven major north-east rivers into two sets — highland and lowland rivers. The highland rivers formed a continuum that could be further divided into rivers with low concentrations of dissolved materials including the Spey and Dee (full highland rivers), and a more variable group with higher concentrations of dissolved materials including the Don, Deveron and Lossie (intermediate highland rivers) emphasising the diversity of river types classically described as highland. The Lossie was differentiated from the other intermediate highland rivers by lower oxygen concentration and pH. The major differences in physicochemistry between rivers were consistent with differences in catchment geology, soil type, climate, and land use. The large amounts of dissolved material and high nutrient status of the lowland Ythan and Ugie rivers reflected the high proportion of their catchments under agriculture, and the acidity of the Lossie reflected the high proportion of its catchment under forest. The small amounts of dissolved material in the Spey and Dee were attributable to the high proportion of slow weathering acidic rocks and acid soils in their catchments, and to the high volume flows of these rivers relative to the others. The amounts of dissolved material were greater in summer during low base flows and were accomparied by an increase in phosphate concentration in the lowland rivers. Oxygen saturation increased in summer in the Ythan and the Don, presumably as a result of greater photosynthetic activity. Marked declines in silica were thought to result from significant diatom growth in the highland and intermediate highland rivers, particularly the Don, during summer.     

Effects of land cover on sediment regime and fish assemblage structure in four southern Appalachian streams

SUMMARY 1. We examined the relationship between catchment land cover, sediment regime and fish assemblage structure in four small streams in the upper Little Tennessee River basin of North Carolina. Study streams drained similar sized catchments (17–31 km²) with different fractions of non-forested land cover. Non-forested land cover was <3% in two 'reference' streams, whereas it was 13 and 22% in two 'disturbed' streams. Land cover data were compared with sediment transport data (suspended and bedload), benthic habitat data (embeddedness, substratum composition and coverage of fines) and fishes collected in autumn 1997.
2. Suspended sediment concentration was significantly higher in disturbed streams during both baseflow and stormflow. During baseflow disturbed streams nearly always exceeded 10 nephelometric turbidity units (NTU), whereas reference streams never exceeded this threshold. The difference in suspended sediment concentration between reference and disturbed streams was more consistent at baseflow than at stormflow. Therefore, baseflow turbidity may be a useful indicator of potential stream degradation.
3. Disturbed sites had five- to nine-fold more bedload transport than reference sites. Both embeddedness and streambed instability increased with increasing non-forested land cover.
4. Relative abundance of fishes requiring clean cobble/gravel substratum for spawning was lower in disturbed streams, whereas relative abundance of mound-building cyprinids, their nest associates and fishes that excavate nests in soft sediments (centrarchids) was higher. Relative abundance of fishes spawning in benthic crevices and gravel (BC + G) declined as the proportion of non-forested land cover increased. This study supports growing evidence that human-induced sedimentation alters stream fish assemblages.     

Phosphorus retention in streams draining pine and hardwood catchments in the southern Appalachian Mountains

SUMMARY. 1. This study was designed to determine how catchment use affects stream phosphorus retention by comparing retention in streams draining three mixed hardwood catchments and three catchments that were planted in white pine in the 1950s.
2. Catchments of similar area and stream discharge were chosen and phosphorus uptake was measured monthly in each catchment along with temperature, discharge, velocity, coarse particulate organic matter (CPOM), fine particulate organic matter (FPOM), and microbial respiration associated with FPOM.
3. On an annual basis, average phosphorus retention was not different between streams draining pine and hardwood catchments nor were there significant differences between physical (temperature, velocity and discharge) or biological (CPOM, FPOM and respiration) parameters based on catchment type. However, discharge was more variable in streams draining pine catchments.
4. Because phosphorus uptake was correlated with discharge, phosphorus retention was also more variable in streams draining pine catchments. Storms caused a greater increar.e in discharge and loss of phosphorus in pine streams than in mixed hardwood streams, but discharge returned to baseline more quickly in pine streams.
5. We suggest that discharge regimes and phosphorus dynamics of streams draining pine catchments are less resistant to change but more resilient than streams draining mixed hardwood forests.     

Catchment land cover as a proxy for macroinvertebrate assemblage structure in Carpathian Mountain streams

We compared land cover, riparian vegetation, and instream habitat characteristics with stream macroinvertebrate assemblages in 25 catchments in the Carpathian Mountains in Central Europe. This study area was particularly selected because of its diverse history of forest and agricultural ecosystems linked to geopolitical dynamic, which provide a suite of unique landscape scale, land cover settings in one ecoregion. Canonical Correspondence Analysis (CCA) showed that variation in composition and structure of macroinvertebrate assemblages was primarily related to four land cover types, and not to riparian or instream habitat. These were the portions in the catchment areas of (1) broadleaved forest, (2) fine-grained agricultural landscape mosaic with scattered trees (e.g., pre-industrial cultural landscape), (3) mixed forest, and (4) natural grassland without trees. Principal Component Analysis (PCA) suggested that land cover types and stream channel substrates co-varied. The PCA also showed that chemical variables, including organic carbon, had higher values in the agricultural landscape compared to natural forests. The major source of variation among taxa in streams was higher abundance of Diptera in agricultural landscapes and of Plecoptera, Coleoptera, Trichoptera, and Amphipoda in forests. Gastropoda and Oligochaeta were more abundant in open, fine-grained agricultural landscape mosaics with scattered trees. Ephemeroptera taxa were quite indifferent to these gradients in catchment land cover, but showed a tendency of being more abundant in the pre-industrial cultural landscape. Our findings suggest that land cover can be used as a proxy of the composition and structure of macroinvertebrate assemblages. This means that land use management at the catchment scale is needed for efficient conservation and recovery of stream invertebrate communities.