Identifying the spatial pattern and importance of hydro‐geomorphic drainage impairments on unpaved roads in the northeastern USA

Roads have been widely studied as sources of runoff and sediment and identified as pollutant production sources to receiving waters. Despite the wealth of research on logging roads in forested, upland settings, little work has been conducted to examine the role of extensive networks of rural, low‐volume, unpaved roads on water quality degradation at the catchment scale. We studied a network of municipal unpaved roads in the northeastern US to identify the type and spatial extent of ‘hydro‐geomorphic impairments’ to water quality. We mapped erosional and depositional features on roads to develop an estimate of pollutant production. We also mapped the type and location of design interventions or best management practices (BMPs) used to improve road drainage and mitigate water quality impairment. We used statistical analyses to identify key controls on the frequency and magnitude of erosional features on the road network, and GIS to scale up from the survey results to the catchment scale to identify the likely importance of unpaved roads as a pollutant source in this setting. An average of 21 hydro‐geomorphic impairments were mapped per kilometer of road, averaging 0.3 m³ in volume. Road gradient and slope position were key controls on the occurrence of these features. The presence of BMPs effectively reduced erosion frequency. Scaled up to the watershed and using a conservative estimate of road–stream connectivity, our results for the Winooski River watershed in the northeastern US suggest that roughly 16% and 6% of the average annual sediment and phosphorus flux, respectively, of the Winooski River may be derived from unpaved roads. Our study identifies an under‐appreciated source of water quality degradation in rural watersheds, provides insights into identifying ‘hot spots’ of pollutant production associated with these networks, and points to effectiveness of design interventions in mitigating these adverse impacts on water quality. Copyright © 2017 John Wiley & Sons, Ltd.     

Creating a thinking space for the rising stars of Australian urban geography

The Institute of Australian Geographers Urban Study Group and Australian Geographer present the first essay in our Leading Insights/Thinking Space partnership. We discuss Dr Natalie Osborne's 2018 essay, flag Dr Marilu Melo's 2019 essay and talk about creating a thinking space for the rising stars of Australian urban geography.     

Species diversity and emergence patterns of nematocerous flies (Insecta: Diptera) from three coastal salt marshes in prince Edward Island, Canada

Emerging insects were monitored every 10 days between early May and late August 1993, from tidal pools in three coastal salt marshes on Prince Edward Island, Canada. The salt marsh pools ranged from about 1 m² to > 1,000 m² in surface area, and had salinities ranging from 11–27‰ Water temperatures through the study period ranged from 4–46°C. Most of the emerging insects were flies (Diptera; 85%), and two-thirds of these were in the sub-Order Nematocera, mainly Chironomidae, Ceratopogonidae, and Culicidae. Forty-three species of Nematocera were identified, although most of these were rare occurrences, and twelve of the species are undescribed. No consistent relationships were found between abundance or diversity and pool size or marsh for Nematocera species overall, although some species showed a statistical preference for a particular marsh or pool size. Emergence patterns were consistent between marshes for species found in different marshes, but overall patterns were highly variable, depending upon species.     

Reconstructing estuarine conditions: oyster shells as recorders of environmental change, Southwest Florida

Live-collected shells of the oyster, Crassostrea virginica, contain geochemical records of modern temperature and salinity, so records of prehistoric conditions may be obtained from subfossil shells. Restoration of channelized watersheds in Florida is receiving much attention, and plans for targeted watersheds require information about estuarine conditions before channelization. Lack of historical records necessitates alternative methods to understand pre-disturbance conditions. A ¹⁴C-calibrated, amino-acid geochronology based on racemization of glutamic acid yielded ages ranging from 190–1220 AD and from 1270–1860 AD for subfossil oysters from Blackwater River (near-natural watershed) and for Faka-Union Bay (channelized watershed), respectively. δ¹⁸O and δ¹³C values of subfossil shells from Blackwater River indicate salinity and summer temperatures similar to present. Winter temperatures recorded in shells from 190, 590, 720, and 1050 AD appear 1–5 °C colder than present winter temperatures, whereas the shell from 1220 AD records winter temperatures similar to modern winter temperatures. These temperature shifts may indicate change in climate or natural seasonal variation of winter temperature from year to year. Subfossils from Faka-Union Bay may reflect a complicated hydrology, which cannot be evaluated by isotopic compositions alone and demonstrates the need for development of independent elemental proxies for temperature and salinity. Decreases in δ¹³C from subfossil to modern shells may in part result from CO₂ added to the atmosphere from fossil fuel burning (the Suess effect). Subfossil δ¹³C that is >1‰ more positive than modern shells suggest a change in the dominant carbon sources from terrestrial C₄ or aquatic plants to C₃ plants (mangroves).     

Recent paleolimnology of three lakes in Northwestern Minnesota

A paleolimnological study was undertaken to investigate changes in three Minnesota lakes over the last 100 years and to demonstrate the stratigraphic effects of cultural eutrophication in two of them. The study combined the analysis of the lake sediment from short cores with stratigraphic analyses of pollen, plant macrofossils, mollusks, diatoms and certain other algae, chydorid Cladocera, and Daphnia ephippia.The rise of Ambrosia type pollen (ragweed) marks the onset of interference with the landscape by European man, which can be closely dated. Calculations of sedimentation rates from this base gave reasonable correlations of other stratigraphic events with historical events.Elk Lake is considered “unpolluted” today and was chosen as a control. Man's effects are limited to logging some of the surrounding forest and to the construction of a dam. Small changes in the lake's fauna and flora are demonstrated, showing the sensitivity of the lake to changes in its catchment area.Lake Sallie and St. Clair Lake, in the same watershed as the city of Detroit Lakes, have been affected not only by logging but also by addition of nutrients from agricultural runoff and sewage effluent. Considerable responses by the lake organisms are apparent. In Lake Sallie the changes were gradual, but in St. Clair Lake they were very abrupt because the lake was partially drained at the same time and the water volume was thereby reduced.The merits of such an integrated study, the types of information gained from the analyses of the various fossils, and the wider application of the results are discussed.     

Cenozoic evolution of the eastern Black Sea: A test of depth-dependent stretching models

Subsidence analysis of the eastern Black Sea basin suggests that the stratigraphy of this deep, extensional basin can be explained by a predominantly pure-shear stretching history. A strain-rate inversion method that assumes pure-shear extension obtains good fits between observed and predicted stratigraphy. A relatively pure-shear strain distribution is also obtained when a strain-rate inversion algorithm is applied that allows extension to vary with depth without assuming its existence or form. The timing of opening of the eastern Black Sea, which occupied a back-arc position during the closure of the Tethys Ocean, has also been a subject of intense debate; competing theories called for basin opening during the Jurassic, Cretaceous or Paleocene/Eocene. Our work suggests that extension likely continued into the early Cenozoic, in agreement with stratigraphic relationships onshore and with estimates for the timing of arc magmatism. Further basin deepening also appears to have occurred in the last ～ 20 myr. This anomalous subsidence event is focused in the northern part of the basin and reaches its peak at ～ 15–10 Ma. We suggest that this comparatively localized shortening is associated with the northward movement of the Arabian plate. We also explore the effects of paleowater depth and elastic thickness on the results. These parameters are controversial, particularly for deep-water basins and margins, but their estimation is a necessary step in any analysis of the tectonic subsidence record stored in stratigraphy.     

Enhancing Community-scale Social Resilience: what is the connection between healthy communities and healthy waterways?

Qualitative research undertaken in a regional centre of northern Queensland revealed how community members with an interest in water quality see themselves and others being pro-active in maintaining healthy waterways. Interview analysis revealed that respondents saw social resilience to changing water quality as contingent upon personal perceptions of water quality; the ability of a whole community to respond to changes in water quality; and individual behaviour change. Many participants explained that, in general, individuals would not take responsibility for maintaining healthy waterways unless there were personal consequences for not acting. We relate these data to current literature linking individual attitudes to community pro-environmental behaviour. We conclude that certain conditions usually prevail before a whole community will take up environmentally responsible behaviour. These conditions include a latent level of social capital, collective social learning, agency coordination, sufficient resources, and personal significance.     

Use of sacrificial embankments to minimize bridge damage from scour during extreme flow events

The leading cause of bridge failure has often been identified as bridge scour, which is generally defined as the erosion or removal of streambed and/or bank material around bridge foundations due to flowing water. These scour critical bridges are particularly vulnerable during extreme flood events, and pose a major risk to human life, transportation infrastructure, and economic sustainability. Retrofitting the thousands of undersized and scour critical bridges to more rigorous standards is prohibitively expensive requiring effective yet economical countermeasures. This research tested the efficacy of using approach embankments as intentional sacrificial “fuses” to protect the bridge integrity and minimize damage during large flow events by allowing the streams to access their natural floodplain and reduce channel velocities. This countermeasure concept was evaluated using the Hydrologic Engineering Center’s River Analysis System models. Steady flow models were developed for three specific bridges on two river reaches. Streamflow return period estimators for both river reaches were developed using Bayesian analysis and available United States Geological Survey stream gauge data to evaluate sacrificial embankments under non-stationary climatic conditions. The use of sacrificial embankments was determined to be a cost-effective scour mitigation strategy for bridges with suboptimal hydraulic capacity and unknown or shallow foundations. Additional benefits of sacrificial embankments include reductions in upstream flood stage and velocity.     

Modelling diatom responses to climate induced fluctuations in the moisture balance in continental Antarctic lakes

The water chemistry of lake systems on the edge of the Antarctic continent responds quickly to changes in the moisture balance. This is expressed as increasing salinity and decreasing lake water level during dry periods, and the opposite during wet periods. The diatom composition of the lakes also changes with these fluctuations in salinity and lake water depth. This is important, as their siliceous remains become incorporated into lake sediments and can provide long-term records of past salinity using transfer functions. In order to develop transfer functions, diatoms and water chemistry data were inter-calibrated from five different East Antarctic oases, namely the Larsemann Hills, the Bølingen Islands, the Vestfold Hills, the Rauer Islands and the Windmill Islands. Results indicate that salinity is the most important environmental variable explaining the variance in the diatom flora in East Antarctic lakes. In oligo- saline lakes the variance is mainly explained by lake water depth. This dataset was used to construct a weighted averaging transfer function for salinity in order to infer historical changes in the moisture balance. This model has a jack-knifed r² of 0.83 and a RMSEP of 0.31. The disadvantage of this transfer function is that salinity changes in oligo-saline lakes are reconstructed inaccurately due to the edge effect and due to the low species turnover along the salinity gradient at its lower end. In order to infer changes in the moisture balance in these lakes, a second transfer function using weighted averaging partial least squares (with two components) for depth was constructed. This model has a jack-knifed r² of 0.76 and a RMSEP of 0.22. Both transfer functions can be used to infer climate driven changes in the moisture balance in lake sediment cores from oligo-, hypo-, meso- and hyper-saline lakes in East Antarctic oases between 102–75°E. The transfer function for lake water depth is promising to track trends in the moisture balance of small freshwater lakes, where changes in shallow and deep-water sediments are readily reflected in changing diatom composition.