Current Hydrological Conditions Research Articles

Current Hydrological Conditions Research of the Chaika lake System in the Territory of the Volga-Akhtuba Floodland

The nature protection measures performed within the national project "Ecology" on the lake system "Chaika" were analysed, the flooding status of the floodland before and after the measures implementation was compared with the equivalent special spring release. A positive effect in increasing the floodland area was confirmed. The chemical analysis results of water and composition of bottom sediments were presented. The bottom sediment was found fertile to be classified as calc-sapropel.

Numerical modelling for ecologically successful spawning-site restoration in Chin-sha River, China

Context The construction of dams on the Chin-sha River will affect fish spawning sites, leading to a decline in fish species. Aims This paper presents a model to evaluate the ecological status of restoration strategies aimed at fish species living at a spawning site. Methods The model comprises hydro-morphodynamic and habitat modules. The modelling approach was applied with two restoration strategies (side-channel addition and riverbank reconstruction) and their corresponding post-restoration effects. Key results Three indicators were utilised to assess the ecological status of the spawning site. Modelling results showed poor ecological status under current hydrological conditions, with weighted usable area and overall suitability index values of 1.07 × 106 m2 and 0.41. Without implementing a restoration strategy, the ecological status would continue to fragment and deteriorate. Conclusions The weighted usable area can be recovered to 2.86 × 106 and 1.67 × 106 m2 in scenarios of side-channel and bank construction respectively. The overall suitability index values increase to 0.67 and 0.63 respectively. Implications It is also noted that the ecological restoration strategy (side-channel addition) can considerably enhance the freshwater Reeves shad’s habitat status. Additionally, the restoration strategy illustrated the feasibility of the side-channel addition restoration strategy.

Assessment of endangered freshwater pearl mussel populations in the Northern Iberian Plateau in relation to non–native species: xenodiversity as a threat

In the last two decades, small populations of freshwater pearl mussels, Margaritifera margaritifera, have been recorded in Mediterranean rivers of the Iberian Northern Plateau. A survey was carried out in Castilla and León in 2018 to assess the development of populations of this species in all the rivers of known distribution and to update the threat classification. Thirty sections in the rivers Negro, Tera, Alberche and Águeda were positive for its presence, and another 50 stretches of seven rivers were negative. The species is currently distributed over about 22.5 km. Águeda and Tera populations have decreased dramatically in the last 14 years and are on the threshold of extinction. The Negro river supports the largest population, although the species has now disappeared in at least 61 % of the stretches that were inhabited in 2004. All populations showed very low densities and an ageing population structure, with no recruitment for decades. The presence of non-native invasive alien species (NIS) was higher than in a previous regional survey, with the signal crayfish representing the greatest threat. We observed changes in benthic microhabitats and direct predation of adults and glochidia conglutinates. In the Alberche River, in strict syntopy with M. margaritifera and two other mussel species, 10 NIS were detected. The current hydrological and ecological conditions in the Duero watershed support the settlement of exotic species to the disadvantage of native mollusks, which are more demanding in terms of microhabitats.

Warming and elevated CO2 promote rapid incorporation and degradation of plant-derived organic matter in an ombrotrophic peatland.

Rising temperatures have the potential to directly affect carbon cycling in peatlands by enhancing organic matter (OM) decomposition, contributing to the release of CO2 and CH4 to the atmosphere. In turn, increasing atmospheric CO2 concentration may stimulate photosynthesis, potentially increasing plant litter inputs belowground and transferring carbon from the atmosphere into terrestrial ecosystems. Key questions remain about the magnitude and rate of these interacting and opposing environmental change drivers. Here, we assess the incorporation and degradation of plant‐ and microbe‐derived OM in an ombrotrophic peatland after 4 years of whole‐ecosystem warming (+0, +2.25, +4.5, +6.75 and +9°C) and two years of elevated CO2 manipulation (500 ppm above ambient). We show that OM molecular composition was substantially altered in the aerobic acrotelm, highlighting the sensitivity of acrotelm carbon to rising temperatures and atmospheric CO2 concentration. While warming accelerated OM decomposition under ambient CO2, new carbon incorporation into peat increased in warming × elevated CO2 treatments for both plant‐ and microbe‐derived OM. Using the isotopic signature of the applied CO2 enrichment as a label for recently photosynthesized OM, our data demonstrate that new plant inputs have been rapidly incorporated into peat carbon. Our results suggest that under current hydrological conditions, rising temperatures and atmospheric CO2 levels will likely offset each other in boreal peatlands.

Hydrogeochemistry Studies in the Oil Sands Region to Investigate the Role of Terrain Connectivity in Nitrogen Critical Loads

Hydrology and geochemistry studies were conducted in the Athabasca Oil Sands region to better understand the water and nitrogen cycles at two selected sites in order to assess the potential for nitrogen transport between adjacent terrain units. A bog—poor fen—upland system was instrumented near Mariana Lakes (ML) (55.899° N, 112.090° W) and a rich fen—upland system was instrumented at JPH (57.122° N, 111.444° W), 100 km south and 45 km north of Fort McMurray, Alberta respectively. LiDAR surveys were initially conducted to delineate the watershed boundaries and topography and to select a range of specific locations for the installation of water table wells and groundwater piezometers. Field work, which included a range of physical measurements as well as water sampling for geochemical and isotopic characterization, was carried out mainly during the thaw seasons of 2011 to 2015. From analysis of the runoff response and nitrogen species abundances we estimate that nitrogen exchange between the wetlands and adjacent terrain units ranged between 2.2 and −3.1 kg/ha/year for rich fens, 0.6 to −1.1 kg/ha/year for poor fens, and between 0.6 and −2.5 kg/ha/year for bogs, predominantly via surface pathways and in the form of dissolved nitrate. A significant storage of dissolved ammonium (and also dissolved organic nitrogen) was found within the pore water of the bog-fen complex at Mariana Lakes, which we attribute to decomposition, although it is likely immobile under current hydrologic conditions, as suggested by tritium distributions. In comparison with the experimental loads of between 5 and 25 kg/ha/year, the potential nitrogen exchange with adjacent terrain units is expected to have only a minor or negligible influence, and is therefore of secondary importance for defining critical loads across the regional landscape. Climate change and development impacts may lead to significant mobilization of nitrogen storages, although more research is required to quantify the potential effects on local ecosystems.

Prognostic and diagnostic assessment of hydrological drought using water and energy budget-based indices

Long-term meteorological drought can lead to hydrological drought by restricting water resources required by humans, such as streamflow and reservoir storage. We developed two new indices for monitoring hydrologic drought-based satellite-derived evapotranspiration, a major factor in hydrological drought occurrence. The Water Budget-based Drought Index (WBDI) estimates potential runoff by the differences between precipitation and evapotranspiration using water budget analysis while the Energy-based Water Deficit Index (EWDI) is an index of available water capacity through evapotranspiration and soil moisture based on solar radiation using energy budget analysis. We used these, along with the existing Standardized Precipitation-Evapotranspiration Index (SPEI, based on precipitation, atmospheric temperature, and evapotranspiration), to map the spatiotemporal patterns of drought on the Korean Peninsula from 2001 to 2014. For validation against actual drought conditions, we compared the results with streamflow data from five gauging stations in South Korea. EWDI—the diagnostic approach—performed best when assessing current hydrological drought conditions, while WBDI and SPEI—prognostic approach—best captured drought conditions after 2–3 months of lag time. Our results confirmed that evapotranspiration is a major factor affecting hydrological drought; the new methods demonstrated here make it possible to evaluate drought through diagnostic and prognostic perspectives depending on the situation, thereby improving scientific drought evaluation capacity.

Root sap flow as a tool to establish hydrological thresholds for plant growth and survival

Water saving technologies are important for sustainable agriculture and forestry. Recent research indicates that the plant itself may alternate between several natural water sources to survive drought. Therefore, a key issue is how to establish the boundaries of hydrological conditions important for non-stressed tree growth. The smart decision might be to ask the plant itself. Sap flow represents a suitable language to such a talk: it gives long-term automatic records of plant responses to environmental changes. In this work we illustrate how root sap flow can be used to provide information on the thresholds for two sources of tree root water uptake, superficial soil water and groundwater. With this knowledge, a threshold diagram can be constructed which is species and site specific. Such a diagram may help managers of rain fed plantations to follow the current hydrological conditions and apply irrigation as a preventive treatment to avoid growth loss and tree mortality.

Calculation of ecological water requirements of urban rivers using a hydrological model: A case study of Beiyun River

The impacts of human activity lead to uncertainty and ambiguity when ecological water requirements (EWRs) are calculated based entirely on the current hydrological conditions of urban rivers, and the requirements for meeting the rivers’ function will also be uncertain. Human activity and river function goals are important factors affecting EWRs. This paper discusses the definition of urban river EWRs and the uncertainties in the results of the calculation, and proposes a calculation method for urban river EWRs that is independent of human activity. The Beiyun River Basin, China, was selected for a case study. The EWRs of the Beiyun River were calculated by combining a precipitation frequency curve with a distributed hydrological model. The rationality of the calculated results was verified using the Tennant method and an evaporation plus seepage calculation for the river. The results of the calculation for the urban river EWRs method proposed in this paper are unique, and the total amount is not affected by human activities. With respect to wet, normal, and dry precipitation frequencies, the minimum, suitable, and ideal EWRs of the Beiyun River are 1.48 × 108 m3, 2.79 × 108 m3, and 3.57 × 108 m3, respectively. The research conclusions are of great significance for the objective determination of the EWRs of urban rivers, and for promoting the appropriate planning and development of urban water.

Safety evaluation of the existing Grawan dam based on hydro-geotechnical behaviour conditions to ensure the availability of water resources

Grawan Dam was built in 2004 to supply irrigation water and raw water. Lately, the dam has experienced various symptoms of damage to the overflow structure due to hydraulic behaviour and the possibility of overtopping of the dam, which endangers the stability of the dam. Therefore, it is necessary to evaluate the overflow structure system based on the current hydrological conditions and to review the slope stability. In this study an evaluation was carried out covering the safety of the slopes as well as the safety of the overflow building system. Dam slope safety was reviewed based on seepage and slope stability. The stability of the overflow structure security system was evaluated in normal and earthquake conditions. The results of the hydrological analysis on guard height, seepage that occurs safely to permit discharge, and slope stability showed 100% safety from permitted safety factors, and on hydraulic conditions resulted in proposed improvements for Vlugter ponds, transition channels, and energy dampers with planning for Q100, Q1000, and QPMF. Analysis for the stability of the overflow structure showed that it is safe against rolling and sliding, and meets the eccentricity and carrying capacity of the soil, being 100% safe.

Proactive water shortage mitigation integrating system optimization and input uncertainty

A complete water shortage mitigation plan which includes water shortage indicators and mitigation measures is essential in adaptive water resources management. Current water shortage triggers used to manage water supply shortages typically recognize only past and current hydrologic conditions and system states, e.g., reservoir storage or water levels. A systematic approach to evaluate the effectiveness of water shortage mitigation measures is often lacked. This study proposes a general framework based on daily simulation-optimization computation scheme to develop water shortage mitigation plan. It includes an innovative simulation-optimization based water shortage trigger framework incorporating both demand and supply side uncertainties to evaluate the state of a water supply system. Stochastically generated demand/supply ensembles were used to simulate system decision variables that were used jointly with past and current hydrologic conditions to prescribe water shortage stages. Each water shortage stage was tied to specific demand and supply side adaptive management actions. A mixed integer programming model optimizing source allocation from surface water harvesting, groundwater production and a desalination plant was then used to minimize operational costs and protect the environment while meeting regional demand. Cumulative mitigation actions were implemented as the system moves progressively to a severe water shortage stage. Retrospective analysis using observed flow and demand in the past decade (2005–2015) was used to vet the approach and demonstrate the advantage of forward looking water shortage trigger development scheme. A combination of mitigation measures is evaluated using stochastic flow and demand in the year 2030, revealing that increased magnitude of groundwater production under severe water shortage situations could be largely (50%) reduced, owing to proactive mitigation actions. The framework was applied to Tampa Bay Water and it has general applications to regional water resources management for utilities across US and beyond.

Modelling the effects of land use and climate change on the water resources in the eastern Baltic Sea region using the SWAT model

Combined and separate impact of climate and land use change on the future river runoff was assessed in the eastern Baltic Sea region by using the SWAT (The Soil and Water Assessment Tool) hydrological model. SWAT was applied to assess how plausible changes in climate and land use may affect the river hydrology by the end of the century. The model was calibrated and validated for a period from 1970 to 2010 (41 years) using daily river runoff data. Statistical and visual analysis of the achieved model presented adequate fit to the observed data allowing the reproduction of the current hydrological conditions of the basins for future analysis. The following conclusions from the study were made: 1) a strong linear correlation between forest cover change and annual river flow change was found; 2) the impact of land use change on runoff is important on an annual scale; 3) the scale of a basin is not important on the hydrological response to forest cover change; 4) the combined effect of land use and climate change was found to be non-additive. Findings of this study would help policy makers, to improve land and water management decisions and in formulating strategies to harness the positive impacts of possible overall increase in river runoff in the north-eastern Baltic Sea region.

Habitat models for assessing river ecosystems and their application to the development of river restoration strategies

ABSTRACTIn this paper, we describe a model system comprised of hydrodynamic, sediment transport, heat transfer and habitat models. We used this model system to assess the ecosystem situation and investigate the impacts of two ecological restoration strategies in the Mian River, China. Freshwater Reeves shad (Tenualosa reevesii) was selected as the target fish species. Model results indicate a low habitat suitability level for T. reevesii under current hydrological conditions. Due to the habitat protection and restoration requirements in China, further numerical model simulations were conducted to investigate the effects of two ecological restoration strategies: addition of a side-channel and riverbank reconstruction (groin field installation). The long-term effects of the restoration projects were also simulated. The analysis indicated that both restoration strategies would significantly enhance the target fish habitat suitability level, with the OSI (overall suitability index) increasing from 39.9% to 53.7% for the added side-channel strategy and from 39.9% to 61.5% for the river bank reconstruction strategy.

Hydrologic Modelling Calibration for Operational Flood Forecasting

Runoff prediction in flood forecasting depends on the use of hydrological simulation models and on the input of accurate precipitation forecasts. Reliability of predictions thus obtained hinges on proper calibration of the model. Moreover, when the model is intended to be used systematically in operational forecasting of streamflows, the calibration process must take into account the variation of the model parameters over time, namely in response to changing weather and hydrological conditions in the basin. The goal of the study was to build a process to adjust, on a daily basis, the simulation model parameters to the current hydrological conditions of the river basin, in order for the model to be run operationally for prediction of the streamflow for the next 10-days period, and, thereby, to forecast the occurrence of flood events. Towards this end, hydrological simulations using the HEC-HMS model were performed, using a 3 h period time step. The present communication focuses on the hydrological model calibration and verification processes and on the evaluation of forecasts’ accuracy. The procedure was applied to a part of the largest (full) Portuguese river basin, the Mondego river basin, corresponding to the Aguieira dam section watershed, which comprises an area of 3070 km2. Four wet periods, associated with the occurrence of flooding, were selected for the calibration and verification of the model, by adjustment of the model parameters. The results of the study aim to define the optimal calibration parameters values to model the observed streamflow for various hydro-meteorological states, thus enabling adequate prediction of flow in flooding situations and proper application of the model in operational flood forecasting.

Towards dynamic flow regime management for floodplain restoration in the Atchafalaya River Basin, Louisiana

This study proposes a novel approach for establishing adaptive environmental-flow prescriptions for rivers, channels, and floodways with substantial flow augmentation and a limited decision space using the highly altered Atchafalaya River Basin (ARB) in Louisiana as an example. Development of the ARB into the primary floodway of the Mississippi River and Tributaries Project has contributed to hydrologic changes basin-wide that have altered the river-floodplain interface threatening important ecosystems, notably the expansive baldcypress-water tupelo swamp forests. Current restoration efforts only address the spatial distribution of water in local areas of the basin; however, the timing, frequency, magnitude, and duration of ecologically-important high and low flows are determined at the basin-wide scale by the daily implementation of a federal flow mandate that limits available water management options. We used current hydrologic conditions and established flow-ecology relationships from the literature to develop an environmental flow prescription for the ARB that provides basin-wide flow targets to complement ongoing restoration efforts. Hydrologic analysis of current flows and the flow-ecology requirements for these wetland forests revealed an overlap in the range of flow variability under the current water management model, suggesting environmental flows can be complementary with the desired hydraulic and geomorphic characteristics of the floodway. The result is a first step towards an adaptive flow regime that strives to balance important flow-ecology relationships within a decision space limited by a federal flow mandate. We found high potential for success in managing water for nature while accommodating other management needs for the river.

Simulation of Green and Blue Water Impacts Caused by Climate Changes in the Apucaraninha River Watershed, Southern Brazil (Simulação dos Impactos da Água Verde e Azul Causados pelas Mudanças Climáticas na Bacia Hidrográfica do Rio Apucaraninha...)

Climate changes may generate significant impacts in the hydrological cycle. It is important to recognize modifications in green water (water stored in soil followed by the consumption of the vegetation) and blue water (water that flows into rivers, lakes, wetlands and shallow aquifers) availability in consequence of climate change modifications. The mathematical modelling is used to simulate the effect of climate change scenarios in hydrological processes in watersheds. This study aimed to evaluate the impacts of climate change in blue and green water in Apucaraninha River Watershed, Southern Brazil, considering the climate scenarios A2 and B2, pessimistic and optimistic, respectively, about greenhouse gases emissions developed by IPCC. SWAT was calibrated and validated using daily streamflow from 1987 to 2012. Climate scenarios A2 and B2 were used to simulate the hydrological conditions for the period 2071-2100. The model presented satisfactory fit compared to the observed data allowing the simulation of the current hydrological conditions, therefore permitting the simulation of future climate change impacts on green and blue water. We found that despite the increase in potential evapotranspiration of 19% and 12% for A2 and B2 scenario respectively, caused by the increase in temperature, the reduction in rainfall amount induced to a reduction in actual evapotranspiration, which correspond to green water, and a reduction of 1% for A2 scenario and 14% for B2 scenario in blue water availability.

Spatial occupancy models for predicting metapopulation dynamics and viability following reintroduction

SummaryThe reintroduction of a species into its historic range is a critical component of conservation programmes designed to restore extirpated metapopulations. However, many reintroduction efforts fail, and the lack of rigorous monitoring programmes and statistical models have prevented a general understanding of the factors affecting metapopulation viability following reintroduction.Spatially explicit metapopulation theory provides the basis for understanding the dynamics of fragmented populations linked by dispersal, but the theory has rarely been used to guide reintroduction programmes because most spatial metapopulation models require presence–absence data from every site in the network, and they do not allow for observation error such as imperfect detection.We develop a spatial occupancy model that relaxes these restrictive assumptions and allows for inference about metapopulation extinction risk and connectivity. We demonstrate the utility of the model using six years of data on the Chiricahua leopard frogLithobates chiricahuensis, a threatened desert‐breeding amphibian that was reintroduced to a network of sites in Arizona USA in 2003.Our results indicate that the model can generate precise predictions of extinction risk and produce connectivity maps that can guide conservation efforts following reintroduction. In the case ofL. chiricahuensis, many sites were functionally isolated, and 82% of sites were characterized by intermittent water availability and high local extinction probabilities (0·84, 95% CI: 0·64–0·99). However, under the current hydrological conditions and spatial arrangement of sites, the risk of metapopulation extinction is estimated to be <3% over a 50‐year time horizon.Low metapopulation extinction risk appears to result from the high dispersal capability of the species, the high density of sites in the region and the existence of predator‐free permanent wetlands with low local extinction probabilities. Should management be required, extinction risk can be reduced by either increasing the hydroperiod of existing sites or by creating new sites to increase connectivity.Synthesis and applications. This work demonstrates how spatio‐temporal statistical models based on ecological theory can be applied to forecast the outcomes of conservation actions such as reintroduction. Our spatial occupancy model should be particularly useful when management agencies lack the funds to collect intensive individual‐level data.

Combining satellite precipitation and long‐term ground observations for hydrological monitoring in China

AbstractSatellite real‐time precipitation enables hydrological monitoring in China where the near‐real‐time ground observations are not readily available. However, the inconsistency between the real‐time satellite precipitation and gauge‐based retrospective data may introduce large systematic bias in near‐real‐time hydrological monitoring. Here we attempted to integrate the Tropical Rainfall Measuring Mission (TRMM) real‐time precipitation (3B42RTV7) into a 62 year gauge‐based retrospective product, the IGSNRR (Institute of Geographical Sciences and Natural Resources Research) dataset through matching their cumulative probability functions toward a near‐real‐time hydrological monitoring consistent with the long‐term retrospective simulations. A nearly 11 year period from March 2000 to December 2010 was taken as the training period to establish the satellite‐gauge precipitation relationship, which was employed in the period of 2011–2013 to evaluate the performance of the adjustment. The results show that the adjusted 3B42RTV7 matches well with IGSNRR precipitation, while the unadjusted data tend to overestimate precipitation. Forced by the adjusted 3B42RTV7, the Variable Infiltration Capacity model can reproduce the IGSNRR‐derived hydrographs and high/low flows better than the model forced by the unadjusted data. The percentiles of the adjusted hydrological estimates in the 62 year estimates from IGSNRR are used for near‐real‐time assessment of hydrological extremes. The hydrological monitoring assisted by the adjusted satellite precipitation, which enables the employment of the long‐term ground observations, is able to capture more detailed drought information than that before adjustment. Our experiment suggests that the satellite real‐time precipitation, after adjustment, can generate the current hydrological conditions which can be directly compared with the long‐term climatology, and thus facilitates near‐real‐time diagnosis and detection of hydrological extremes.

Simulation of hydrosedimentological impacts caused by climate change in the Apucaraninha River watershed, southern Brazil

Abstract. Climate change can cause significant modifications in hydrosedimentological processes. Climate projections indicate the occurrence of extreme events, in terms of precipitation, droughts, floods and temperature. By increasing temperatures and altering precipitation regimes, climate change is expected to affect sediment dynamics. Predictions of the effects of climate change on streamflow and sediment yield vary widely, depending on the geographical location and climate scenarios used. Mathematical modelling can be used to simulate the hydrosedimentological processes in watersheds and enable the simulation of climate change effects on sediment yield. This paper aims to simulate the impacts of climate change hydrosedimentological dynamics in the Apucaraninha River watershed (504 km²), southern Brazil, considering the climate change scenarios A2 (pessimistic about the emissions of greenhouse gases) and B2 (optimistic about the emissions of greenhouse gases), developed by the IPCC. The Soil and Water Assessment Tool (SWAT) was used to evaluate the impacts of climate projections on the sediment yield in the Apucaraninha River watershed. The model was calibrated and validated using daily streamflow and sediment data from 1987 to 2012. The model presented satisfactory fit to the observed data allowing the reproduction of the current hydrological conditions of the watershed. Based on the satisfactory results in calibration and validation, the climate scenarios A2 and B2 were inserted to simulate streamflow and sediment conditions for the period 2071–2100. The results for both scenarios indicate that simulations of both climate scenarios resulted in changes in hydrosedimentological dynamics in the Apucaraninha River watershed, mainly in terms of decrease in average sediment yield due to the reduction in precipitation amount and increase in evapotranspiration. Our results also indicate that every 1% change in precipitation has resulted in 2.8% change in soil erosion and 1.6% change in runoff under scenario A2, and 2.3% change in erosion and 1.1% in runoff under scenarios B2, thus suggesting that climate change tends to affect sediment yield more than streamflow, although seasonally both could be impacted in similar ways.

Water Data Systems: Science, Practice, and Policy

Water agencies, governmental organizations, and non-governmental organizations accountable for water use, development, and conservation are dealing with ways to address changes in water data collection, maintenance, storage, visualization, and communication. As demand for water resources and variability of water availability increases, water data are essential to monitoring changes and finding solutions. Coupled with other data efforts to enhance “big data” and serve critical environmental issues, water data reveal the complex data-scape that demands streamlined data standards across scientific communities where data processing systems are fragmented due to multiple sources and methodologies, limited data sharing, and incomplete data coverage. With a better understanding of some of the discrepancies in the science, practice, and policy of water data systems, we need to consider and implement innovative ways to foster stronger water data sharing arrangements. This special issue on Water Data explores the science, practice, and policy of water data systems, provides examples in which data integration has been successful or ineffective, and explores the technological frontier of water data systems.

Interannual drought length governs dissolved organic carbon dynamics in blackwater rivers of the western upper Suwannee River basin

AbstractThe Little River (LR) in southern Georgia, U.S., has experienced lengthening droughts since monitoring began in 1972. We evaluated the impacts of drought on riverine carbon cycling using a 9 year data set of dissolved organic carbon (DOC) coupled with laboratory experiments in the LR, as well as long‐term data sets in three additional rivers within the Suwannee River basin. Longer drought periods reduced downstream DOC export but also led to higher DOC concentrations in the following hydroperiod. Within a hydroperiod, DOC concentration was positively correlated with temperature and negatively correlated with river discharge but also negatively correlated with total discharge during the previous hydroperiod. Among hydroperiods, DOC concentration was more strongly correlated with antecedent hydrological conditions than with current hydrological conditions across broad spatial scales: in three additional rivers within the Suwannee River basin (Alapaha, Withlacoochee, and Okapilco) and in headwater and downstream reaches of the LR. Microbial DOC consumption and CO2 production were elevated when DOC concentration was high. Despite dramatic hydrologic changes, DOC composition appeared stable, with optical analyses suggesting that LR DOC is primarily composed of three terrestrial humic‐like fluorescence groups. If the current climatic trend of intensifying droughts, elevated temperatures and decreased discharge continue, our results suggest the net effect may be for a more localized riverine carbon cycle with reduced downstream transport of DOC, but higher local mineralization rates due to elevated DOC concentrations.