Jason P. Julian

Suspended sediment, dissolved organic carbon, and dissolved nitrogen export during the dam removal process

[1] Total suspended solids (TSS), dissolved organic carbon (DOC), and total dissolved nitrogen (TDN) loads were calculated for all stages of the dam removal process (dewatering, breaching, and removal) at various points upstream, within, and downstream of Lowell Mill Impoundment on the Little River, North Carolina. The impoundment dewatering exported loads of TSS, DOC, and TDN which were all 1–2 orders of magnitude less than loads associated with historic floods. Conversely, floods exiting the former impoundment following dam removal produced TSS, DOC, and TDN loads comparable to, but slightly greater (1.2–1.75 times) than historic floods. Exported loads were greatest following the complete removal of the dam, most likely because of increased channel gradient. We assert that the disturbances (i.e., concentrations and loads) associated with dam removal should be compared to those generated by floods within the same system rather than comparing the impacts of dam removal with base flow conditions. During the dewatering, impounded floodplain wetlands were found to contribute the following percentages to total impoundment loads: 44% of stored water, 12.6 % of TSS, 49% of DOC, and 33% of TDN. Moreover, the dewatering flood wave was sampled at various points along a 19.2-km reach below the dam to characterize the routing of TSS, DOC, and TDN. TSS released by the impoundment was retained within 10 km of the dam, while TDN and DOC loads increased slightly. Finally, we used our results with those from other removals to provide insight into regional and morphologic controls on exports of impounded materials following dam removal.

Drought-induced changes in flow regimes lead to long-term losses in mussel-provided ecosystem services

Extreme hydro-meteorological events such as droughts are becoming more frequent, intense, and persistent. This is particularly true in the south central USA, where rapidly growing urban areas are running out of water and human-engineered water storage and management are leading to broad-scale changes in flow regimes. The Kiamichi River in southeastern Oklahoma, USA, has high fish and freshwater mussel biodiversity. However, water from this rural river is desired by multiple urban areas and other entities. Freshwater mussels are large, long-lived filter feeders that provide important ecosystem services. We ask how observed changes in mussel biomass and community composition resulting from drought-induced changes in flow regimes might lead to changes in river ecosystem services. We sampled mussel communities in this river over a 20-year period that included two severe droughts. We then used laboratory-derived physiological rates and river-wide estimates of species-specific mussel biomass to estimate three aggregate ecosystem services provided by mussels over this time period: biofiltration, nutrient recycling (nitrogen and phosphorus), and nutrient storage (nitrogen, phosphorus, and carbon). Mussel populations declined over 60%, and declines were directly linked to drought-induced changes in flow regimes. All ecosystem services declined over time and mirrored biomass losses. Mussel declines were exacerbated by human water management, which has increased the magnitude and frequency of hydrologic drought in downstream reaches of the river. Freshwater mussels are globally imperiled and declining around the world. Summed across multiple streams and rivers, mussel losses similar to those we document here could have considerable consequences for downstream water quality although lost biofiltration and nutrient retention. While we cannot control the frequency and severity of climatological droughts, water releases from reservoirs could be used to augment stream flows and prevent compounded anthropogenic stressors.

Potential Stream Density in Mid-Atlantic U.S. Watersheds

Stream network density exerts a strong influence on ecohydrologic processes in watersheds, yet existing stream maps fail to capture most headwater streams and therefore underestimate stream density. Furthermore, discrepancies between mapped and actual stream length vary between watersheds, confounding efforts to understand the impacts of land use on stream ecosystems. Here we report on research that predicts stream presence from coupled field observations of headwater stream channels and terrain variables that were calculated both locally and as an average across the watershed upstream of any location on the landscape. Our approach used maximum entropy modeling (MaxEnt), a robust method commonly implemented to model species distributions that requires information only on the presence of the entity of interest. In validation, the method correctly predicts the presence of 86% of all 10-m stream segments and errors are low (<1%) for catchments larger than 10 ha. We apply this model to the entire Potomac River watershed (37,800 km2) and several adjacent watersheds to map stream density and compare our results with the National Hydrography Dataset (NHD). We find that NHD underestimates stream density by up to 250%, with errors being greatest in the densely urbanized cities of Washington, DC and Baltimore, MD and in regions where the NHD has never been updated from its original, coarse-grain mapping. This work is the most ambitious attempt yet to map stream networks over a large region and will have lasting implications for modeling and conservation efforts.

Social Demand for Ecosystem Services and Implications for Watershed Management

We performed a sociocultural preference assessment for a suite of ecosystem services provided by the Kiamichi River watershed in the south-central United States, a region with intense water conflict. The goal was to examine how a social assessment of services could be used to weigh tradeoffs among water resource uses for future watershed management and planning. We identified the ecosystem services beneficiaries groups, analyzed perception for maintaining services, assessed differences in the importance and perceived trends for ecosystem services, and explored the perceived impact on ecosystem services arising from different watershed management scenarios. Results show habitat for species and water regulation were two ecosystem services all beneficiaries agreed were important. The main discrepancies among stakeholder groups were found for water-related services. The identification of potential tradeoffs between services under different flow scenarios promotes a dynamic management strategy for allocating water resources, one that mitigates potential conflicts. While it is widely accepted the needs of all beneficiaries should be considered for the successful incorporation of ecosystem services into watershed management, the number of studies actually using the sociocultural perspective in ecosystem service assessment is limited. Our study demonstrates it is both possible and useful to quantify social demand of ecosystem services in watershed management.

Optical Water Quality of Inland Waters: A Landscape Perspective

Optical water quality (OWQ) relates the composition of waters to their light transmission and thereby light availability for aquatic plants, visual range for aquatic animals, and suitability for recreational uses. This fundamental role of OWQ has led to numerous studies on the optical properties in rivers and lakes, which we overview here with a landscape perspective. International examples illustrate how the kinds and amounts of light-attenuating substances depend on landscape features on scales ranging from the river reach to the orientation of mountain ranges. OWQ is profoundly affected by increased nutrient discharges and sediment mobilization from human activities such as agriculture. Proper monitoring of OWQ is needed to fully understand and address these consequences. Remote sensing has potential for broad-scale surveys of OWQ, although currently its applications to inland waters are limited by low spatial resolution. A better understanding of OWQ will advance water management and remote sensing capabilities, as well as provide further insight into water quality impacts associated with global changes in climate, energy use, and land use.

Long-term impacts of land cover changes on stream channel loss.

Land cover change and stream channel loss are two related global environmental changes that are expanding and intensifying. Here, we examine how different types and transitions of land cover change impact stream channel loss across a large urbanizing watershed. We present historical land cover in the 666-km(2) Lake Thunderbird watershed in central Oklahoma (USA) over a 137 year period and coinciding stream channel length changes for the most recent 70 years of this period. Combining these two datasets allowed us to assess the interaction of land cover changes with stream channel loss. Over this period, the upper third of the watershed shifted from predominantly native grassland to an agricultural landscape, followed by widespread urbanization. The lower two-thirds of the watershed changed from a forested landscape to a mosaic of agriculture, urban, forest, and open water. Most channel length lost in the watershed over time was replaced by agriculture. Urban development gradually increased channel loss and disconnection from 1942 to 2011, particularly in the headwaters. Intensities of channel loss for both agriculture and urban increased over time. The two longest connected segments of channel loss came from the creation of two large impoundments, resulting in 46 km and 25 km of lost stream channel, respectively. Overall, the results from this study demonstrate that multiple and various land-use changes over long time periods can lead to rapid losses of large channel lengths as well as gradual (but increasing) losses of small channel lengths across all stream sizes. When these stream channel losses are taken into account, the environmental impacts of anthropogenic land-use change are compounded.

Land Cover Heterogeneity Effects on Sub-Pixel and Per-Pixel Classifications

Abstract: Per-pixel and sub-pixel are two common classification methods in land cover studies. The characteristics of a landscape, particularly the land cover itself, can affect the accuracies of both methods. The objectives of this study were to: (1) compare the performance of sub-pixel vs. per-pixel classification methods for a broad heterogeneous region; and (2) analyze the impact of land cover heterogeneity ( i.e. , the number of land cover classes per pixel) on both classification methods. The results demonstrated that the accuracy of both per-pixel and sub-pixel classification methods were generally reduced by increasing land cover heterogeneity. Urban areas, for example, were found to have the lowest accuracy for the per-pixel method, because they had the highest heterogeneity. Conversely, rural areas dominated by cropland and grassland had low heterogeneity and high accuracy. When a sub-pixel method was used, the producer’s accuracy for artificial surfaces was increased by more than 20%. For all other land cover classes, sub-pixel and per-pixel classification methods performed similarly. Thus, the sub-pixel classification was only advantageous for heterogeneous urban landscapes. Both creators and users of land cover datasets should be aware of the inherent landscape heterogeneity and its potential effect on map accuracy.

Disturbance analyses of forests and grasslands with MODIS and Landsat in New Zealand

Abstract In this study we present, evaluate and validate an approach to monitor forest and grassland disturbance. We apply the approach to both Landsat and MODIS imagery for the North Island of New Zealand and validate the results based on high resolution OrbView and Ikonos imagery. We found an overall accuracy of the disturbance index of 98% for the two studied land cover types. The kappa value was 0.770 indicating a 77% better agreement than what would have occurred by chance. We found that there is a difference between the accuracy received for grassland areas compared to the accuracy received for forest areas, with the grassland areas outperforming the forest areas (Kappa of 0.855 vs. 0.656). We split the validation results by soil type and also evaluate the effect of different soil types with respect to grazing pressures. The disturbance index behaved consistently for all available soil orders. We found forest disturbance for approximately 36.2% of the exotic forests, resulting in an annual clearing rate of 2.6% of the forest over the study period. Lastly we present a close-up study to evaluate the changes in grazing in one intensely used catchment. We demonstrate that the December/January disturbance rates have increased from about 6% in 2000 to about 16% in 2012.

Shaping the Physical Template: Biological, Hydrological, and Geomorphic Connections in Stream Channels

Abstract Stream channels are scaled to the amount of water and sediment they convey. The amount and size of bed sediment, composition of bank material, type of channel vegetation (both riparian and in-stream), and valley morphology (slope and width) influence channel size and shape. Interactions and feedbacks among these six bio-hydro-geomorphic controls dictate channel stability and how channels respond to changes in the environment. In this chapter, we use these six interdependent variables as context in which to demonstrate how connections among hydrology, geomorphology, and vegetation; (1) set the range of variability in channel morphology; (2) understand disturbance-recovery regimes in streams; (3) illustrate how bio-hydro-geomorphic templates influence important abiotic components of stream ecosystems; and (4) present management strategies that incorporate bio-hydro-geomorphic connections. Finally, we discuss some of the important challenges that lay ahead in connecting fluvial geomorphology and stream ecology.

The Impact of Past and Future Urban Expansion on Soil Resources in Central Arkansas, 1994–2030

As cities expand, activities associated with urban growth disturb and seal soil resources. Urban processes compact, move, deposit, and contaminate soils, affecting local soil ecosystems and environmental quality at increasing scales. This article offers a spatially explicit account of the impact of urban expansion on soil resources in central Arkansas from 1994 to 2030 and proposes a conceptual framework that situates the impacts of urbanization on soil resources at multiple scales. We analyzed three soil characteristics (available water storage, agricultural productivity, and soil organic carbon) in the context of urban growth patterns over a 10,000 km2 study area centered on the capital of Little Rock. From 1994 to 2011, urbanization occurred near primary transportation networks and existing urban centers. From 2011 to 2030, urban growth will likely expand along the transportation corridors into the Ouachita Mountains and Arkansas Valley. By 2030, we estimate that urbanization will affect 10 percent of the regions soil resources with varying impacts on soil quality and quantity. Our results provide place-specific knowledge of soil disturbance, which is useful for creating policies and initiatives to mitigate degradation of soil resources with increasing urbanization.