Spatial and seasonal variations in δ13C AND δ15N of particulate organic matter in a dam‐controlled subtropical river

Alteration of stream flow by artificial dams has been observed to be a significant factor for river water environmental changes. Therefore, understanding the biogeochemical processes occurring in the dam‐controlled rivers is important for water resource management. In this paper, δ¹³C and δ¹⁵N signatures of particulate organic matter (POM) in a dam‐controlled subtropical river, Beijiang River, in south China are reported for their spatial and seasonal distributions. POM affected by reservoirs is lighter in δ¹³C and heavier in δ¹⁵N relative to unaffected POM. In April, POM δ¹³C and δ¹⁵N values show less spatial variation in the mainstem, and suggest relatively greater contributions of terrestrial organic matter (OM) to POM. This could be related to the onset of summer monsoon that caused an abrupt increase in terrestrial input to the river by the monsoon‐induced enhancement of rainfall and runoff. In August and December, however, POM isotopic values for the sites affected by the Feilaixia dam reservoir in the middle of the river show marked changes, suggesting aquatic plankton proliferation in the reservoir during the times. Upstream from the reservoirs, POM isotopes are seasonally less varied and suggest mainly terrestrial origin. However, the isotopic signals of aquatic plankton proliferation in the reservoir in August and December is imprinted on the POM isotopic compositions downstream the reservoir, indicating far‐reaching influences of the reservoir on the downstream water environment. Copyright © 2008 John Wiley & Sons, Ltd.     

Stream regulation and nitrogen dynamics in sediment interstices: comparison of natural and straightened sectors of a third‐order stream

Nitrogen dynamics were studied in the interstitial environment (i.e. hyporheic zone) of a sandy‐bottom stream in a rural landscape. A third‐order stream in Brittany (France) was studied at 11 stations (riffles) to evaluate spatial patterns of water exchange between surface and interstitial habitats. More intensive sampling was conducted in three riffles selected according to their hydrological characteristics. Chemical characteristics (especially nitrogen) and microbial denitrification were studied at 12.5 and 25 cm depth upstream, and 25 cm depth downstream of each riffle. This study confirms that the interstitial habitat of a N‐rich stream acts as a sink for the nitrate‐nitrogen. Experimental manipulation of sediment cores indicates that denitrification is limited by carbon in surface (i.e. benthic) and by nitrate in hyporheic sediments. River regulation increases inputs of fine sediments, modifies river channel location, and generates changes in the spatial patterns of biogeochemical processes, water origins, and hydrologic exchanges. Copyright © 2004 John Wiley & Sons, Ltd.     

Organic matter transport and retention in a blackwater stream recovering from flow augmentation and thermal discharge

Organic and inorganic seston, benthic organic matter and woody debris were studied in a blackwater stream/floodplain system recovering from flow augmentation and thermal discharges. The stream had received cooling waters from two nuclear reactors from the mid-1950s to 1968, resulting in flows over 10x greater than normal and temperatures that exceeded 70°C. Channel morphology was markedly altered, woody debris was removed or buried, and floodplain vegetation was destroyed. Fifteen years after termination of cooling water discharges, the stream continued to exhibit many characteristics of a disturbed system. Compared to an undistributed reference stream, the recovering stream had substantially less benthic organic matter, fewer snags and debris dams, and transported more organic and inorganic seston of all size fractions examined. Because of the importance of these biophysical factors in the structural morphology of blackwater streams, it is hypothesized that complete recovery will not be realized until the floodplain forest has matured and large woody debris is contributed to the stream channel.     

Dissolved and particulate organic carbon concentrations in stream water and relationships with land use in multiple-use watersheds of the Han River (Korea)

This study examines temporal variation in dissolved organic carbon (DOC) and particulate organic carbon (POC) concentrations in streams in the Han River watershed, Korea. On days without significant antecedent rain, DOC and POC concentrations ranged from 0.87 to 3.23 mg C/L and 0.24 to 2.92 mg C/L, respectively. Following rain events, both DOC and POC concentrations were higher. Soil and compost had δ¹³C values similar to stream δ¹³C-DOC and δ¹³C-POC. These results demonstrate the importance of studies using tracer approaches and the value of research on sources of organic carbon transported in streams in multiple use monsoonal watersheds.     

Effectiveness of braided,gravel‐bed river restoration in the Upper Waitaki Basin,New Zealand

In 1991 the New Zealand Department of Conservation implemented Project River Recovery (PRR) to restore braided, gravel‐bed riverine and wetland habitats in the Upper Waitaki Basin on the South Island. These are critical habitats for wading and shore birds, including threatened species, but have been degraded by hydroelectric power development. This paper evaluates the effectiveness of PRR after more than 10 years with regard to key issues, effective methods, and lessons learned. Few restoration programs explicitly include evaluation of effectiveness or criteria for success, thereby limiting knowledge transfer and benefits to new or ongoing projects. This evaluation is based on site visits, interviews with program staff, review of PRR documents, comparisons with international restoration programs and recommendations, and a Strengths, Weaknesses, Opportunities, and Threats (SWOT) analysis. Primary components include pest plant and animal control, wetland construction and enhancement, research and monitoring, and public awareness. The program has elements common to many other restoration programs, including strategic planning and annual reporting. Its strengths include well‐defined goals, stakeholder collaboration, and successful integration of science with restoration as part of adaptive management. PRR could benefit from improved understanding of physical and watershed characteristics, expansion of goals at multiple scales, additional collaboration with other organizations, and knowledge transfer. Threats include weed invasions and increased recreational and land‐use impacts. Copyright © 2006 John Wiley & Sons, Ltd.     

The distribution and turnover of benthic organic matter in a lowland river: influence of hydrology,seston load and impoundment

The standing stocks of benthic organic matter (BOM) and some of its biochemical compounds (particulate organic carbon, particulate nitrogen, protein, and chlorophyll a) were investigated in the upper 12 cm of the sediments at several sampling sites in a free‐flowing and in an impounded river section of the lowland River Spree (Germany). Several environmental variables were recorded, in order to determine their potential influence on the organic matter content in the sediments. It was shown that the organic matter content in the upper sediment layers was mainly determined by the local hydrological regime, which was best reflected by the particle size distribution at the sampling sites. For the deepest investigated sediment strata, no influencing factors could be determined. The amount and quality of suspended matter was of minor importance to sediment composition. Also seasonal effects could not be detected. The impounded river section exhibited less seasonal variation in organic matter storage, as well as shorter carbon turnover lengths, longer carbon turnover times and lower rates of annual organic matter recycling than the free‐flowing river section, which indicates that changes in river hydraulics result in alterations to the organic matter budget. These alterations could be related to the changed mesohabitat composition and to the higher standing stocks of organic matter in the impounded river reach. We conclude that both morphological and hydrological alterations affect the structure and function of running water ecosystems because of their negative effect on the organic matter cycling. Copyright © 2002 John Wiley & Sons, Ltd.     

Fluorescence analysis of dissolved organic matter in natural,waste and polluted waters—a review

Dissolved organic matter (DOM) in aquatic systems originates from a range of sources. Some is allochthonous, transported from the surrounding landscape to the water body, and is derived from and influenced by the geology, land use and hydrology of its origin. Some is created in situ through microbial activity, which may provide an independent source of organic matter, or a recycling mechanism for that which has been transported into the water body. The relative contribution of each source depends upon the location and environmental conditions within and without the water body. Human activity is also a source of DOM, much of which is believed to be labile, which can enter the aquatic system through direct point discharges, diffuse leaching and aerial dispersal. Fluorescence spectroscopy can provide an excellent tool to source DOM fractions, and to monitor and understand DOM transformations in aquatic systems, as much DOM has an intrinsic fluorescence. In particular, recent advances in optical technology, enabling rapid investigation of shorter wavelengths, have enabled more detailed characterization of organic material and its reactions in water. In this article, we review the use of fluorescence spectroscopic techniques to measure the intrinsic fluorescence of organic matter and the application of fluorescent DOM analysis in marine waters, freshwaters and wastewaters. Copyright © 2007 John Wiley & Sons, Ltd.     

Turbidity and dissolved organic matter as significant predictors of spatio‐temporal dynamics of phosphorus in a large river‐floodplain system

Phosphorus (P) inputs are increasing in river‐floodplain systems, but the factors which influence the dynamics of this nutrient are not clear. To assess P dynamics in this kind of river, the main channel of the Middle Paraná River, 3 anabranches, 9 secondary channels, and 20 lakes (7 permanently connected and 13 temporarily connected to the fluvial system) were sampled. Multiple linear regressions were applied to explain spatio‐temporal patterns of P through commonly measured limnological variables. Particulate P increased during the sediment peak (evaluated through turbidity). Soluble reactive P (SRP) was positively associated with dissolved organic matter (DOM, mainly the chromophoric fraction), which increased during high waters in the fluvial system but was highly variable in each kind of aquatic environment. In temporarily connected lakes, vegetated zones dominated by emergent macrophytes displayed the highest SRP and chromophoric DOM concentrations. The flood and sediment peak positively affected P load in the river due to the increase in dissolved and particulate fractions, respectively. In addition, particle‐bound alkaline phosphatase activity was positively associated with SRP concentration and load. These results suggest that the sediment peak incorporates particulate P in the system while the floodplain is a P source during floods through exportation of the dissolved fraction. Dissolved P could be largely exported associated with DOM, which stimulates phosphatase biosynthesis by decreasing P bioavailability. The effect of aquatic macrophytes on P dynamics seems to be influenced by DOM exudation. According to these considerations, DOM should be taken into account to analyse P dynamics in river‐floodplain systems.     

基于GOCI影像反演湖泊悬浮物和叶绿素a含量的研究述评

悬浮颗粒物和叶绿素a是两个重要的湖泊水质参数,常用来衡量湖泊的富营养化程度。阐述了基于GOCI数据的湖泊悬浮颗粒物和叶绿素a浓度反演的研究现状,分析了几种大气校正方法对于GOCI数据的适宜性,发现基于6S模型的大气校正取得的效果最好。对比了GOCI的几种用于叶绿素a和悬浮颗粒物反演的模型,发现基于经验方法的反演虽然简单易行,但缺乏物理依据;基于分析方法的反演机制明确,但较难实现;基于半分析方法的反演是统计水质参数的光谱特征,建立遥感数据的波段组合与水质参数值之间的定量关系,进而估算水质参数含量,此方法较易实现且有一定物理意义。最后,通过总结现状,对利用GOCI反演水体指标的发展提出了一些自己的见解。     

Consumer‐diet discrimination of δ13C and δ15N: Source‐ and feeding‐oriented patterns based on gut content analysis in a large subtropical river of China

Understanding the trophic discrimination (?¹³C and ?¹⁵N) between consumers and diets in fluvial systems remains difficult because of the variable food sources and complex predator–prey interactions from headwaters to the estuaries. Here, stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes in fish and invertebrates from a large subtropical river in southern China were determined to explore trophic discrimination in conjunction with a gut content analysis. The ?¹³C values showed significant differences (p < .05) among functional feeding groups, with fish, shrimp, and insect scrapers presenting higher ?¹³C values (1.20 ± 0.23‰ to 1.51 ± 0.31‰) than other groups. The ?¹⁵N values varied significantly between invertebrates (0.64 ± 0.17‰ of insect collector‐gatherers to 1.63 ± 0.36‰ of shrimp predators) and fish (1.98 ± 0.19‰ of detritivores to 2.71 ± 0.43‰ of crustaceavores) and exhibited an increasing tendency from primary to secondary consumers. A linear regression analysis revealed that the longitudinal changes in ?¹³C and ?¹⁵N were closely associated with the δ¹³C of periphyton, the δ¹⁵N of particulate organic matter (POM) in water, and the relative contribution (%) of periphyton and organic detritus to the diet composition of consumers. These results indicated that discrimination factors might not only be influenced by the isotope signatures of basal food sources but also downstream shifts in dominant food items utilized by consumers. In particular, trophic discrimination between periphyton– and detritus–based food chains, such as “epilithic diatoms–shrimp scrapers–crustaceavorous fish” and “POM–bivalves–molluscivorous fish,” displayed regionally specific patterns. When back‐calculating to the diet assimilation and trophic position in subtropical streams and rivers, we suggest using the basin‐scale ?¹³C value of 0.96 ± 0.26‰ for all consumers and ?¹⁵N values of 1.07 ± 0.32‰ for invertebrates and 2.38 ± 0.37‰ for fish.     

Calibration of turbidity meter and acoustic doppler velocimetry (Triton‐ADV) for sediment types present in drained peatland headwaters: Focus on particulate organic peat

Suspended sediments have a clear impact on fluvial water quality and aquatic habitats. As the concentrations are highly variable, continuous measurement offers a good way to provide accurate and precise values of sediment concentration and yield. However, there is a lack of information regarding the effect of organic peat particles, which typically appear in boreal fluvial systems. In the present study, the effect of different types of suspended sediments on calibration of a turbidity meter and an acoustic Doppler velocimetry (Triton‐ADV) was studied in laboratory conditions. The measurements were performed using particulate organic peat, clay and silt with several concentrations ranging from clear water to 3500 mg L^?1. The present study primarily provides organic peat sediment calibration data for used sensors. Regression equations were developed for the different sediment. The results indicate that particle size, shape, concentration and sediment type have an effect on calibration. When the turbidity and the ADV calibration were performed for different particle size groups, sediment types and concentrations, the calibration and suspended solids calculation error was reduced. For the turbidity sensor used, the reliable upper continuous measurement limit for clay, peat and silt sediments was found to be at 1000, 2500 and 3500 mg L^?1, respectively. The ADV‐sensor was noticed to be reliable only with fine particles. The results enable easy and first step calibration and error assessment for automatic turbidity and acoustic monitoring of the suspended sediment quality typically present in headwater fluvial systems. This study can be used to evaluate the effect of different sediments on turbidity and ADV‐measuring error and reliability during changing particles size distributions, characteristics and concentrations. The laboratory‐based approach used in this study indicates that the shape of organic peat particles has an influence on sensor calibration, especially when suspended sediment concentrations are high. Copyright © 2009 John Wiley & Sons, Ltd.     

A multi‐tracers analysis of sources and transfers of particulate organic matter in a tropical reservoir (Petit Saut,French Guiana)

We measured the organic carbon (OC) content, the isotopic composition, the C/N ratios and the photosynthetic pigment composition of suspended matter, sediments, sediments traps and epiphytic and epilithic biofilms at the tropical Sinnamary River system (French Guiana). Our sampling included the mid‐stream reservoir lake (Petit Saut) and the estuary on the Atlantic coast. These tracers were complementary and allowed identifying different sources of particulate organic matter (POM) in the system. We found a δ¹³C–C/N signature of POM close to that of soils and litters collected in the surrounding forest, both for water column and sediment at the upstream station as well as for the sediment in a littoral zone of the reservoir, which thus indicated a terrestrial origin. Plankton communities at the centre of the reservoir were dominated by Chlorophyceae (chlorophyll a (Chl a), chlorophyll b (Chl b) and lutein) in the oxic epilimnion and by anoxygenic phototrophic bacteria, namely Chlorobiaceae (bacteriochlorophyll d (BChl d) and bacteriochlorophyll c (BChl c)) at and below the oxycline (6 m depth). In addition, this planktonic material was slightly ¹³C‐depleted due to a contribution of methanotrophic bacteria. Phytoplankton and bacterioplankton were the major source of settling material collected in the traps at all depths in the centre of the reservoir. In the traps, POM was subject to intense degradation, as revealed by C/N and isotopic data and by the presence of pheopigments. In the river downstream of the dam, Chl b, lutein, BChl c and d originating from the reservoir progressively decreased downstream as the result of mineralization. At the estuarine mouth, fucoxanthin showed the presence of diatoms and the δ¹³C‐C/N signature matched that of POM carried by the Amazonian coastal mobile mud belt. By analysing sedimentation rates in the reservoir and its outflow into the river, we were able to provide a first estimates of POM transfers in this system during the sampling period. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of Hydrological Connectivity on Plankton Communities in Natural and Reconstructed Side‐Arms of a Large New Zealand River

We sampled natural and reconstructed side‐arms during different stages of hydrological connectivity with a large floodplain river in northern New Zealand, to determine whether re‐establishment of connectivity would be an effective strategy for restoring plankton communities in former side‐arms. Connectivity between side‐arms and the river was moderated by water level and influenced flow rates and closure of inlets and outlets. Physicochemical conditions were more strongly related to the connectivity phase than to habitat type (river, natural or reconstructed side‐arm), except during low connectivity when natural side‐arms in particular were characterised by higher ammonium (NH₄‐N) and total phosphorus (P) concentrations, as well as specific conductivity. Dissolved reactive phosphorus (PO₄‐P), water temperature, conductivity and dissolved oxygen were identified as explanatory variables of phytoplankton and zooplankton community composition, which along with total nitrogen (phytoplankton) or total suspended solids (zooplankton) explained 44–52% of variation. Phytoplankton community composition and the abundance of several dominant or discriminatory taxa were affected by connectivity but not habitat type, whereas habitat and connectivity both had significant effects on zooplankton communities and abundances of the cladoceran Bosmina meridionalis. Significant interactions between connectivity and paired habitat types occurred for abundances of the diatom Asterionella, the cryptophyte Cryptomonas, the rotifer Synchaeta oblonga and cyclopoid copepods, reflecting differential responses to connectivity among habitats by these taxa. Overall, these results underscore the importance of hydrological connectivity between side‐arms and rivers in moderating plankton community composition, and highlight unpredictable trajectories of community development and alternative transient states that can occur soon after side‐arm reconnection. Copyright © 2016 John Wiley & Sons, Ltd.