Drivers of interannual and intra‐annual variability of dissolved organic carbon concentration in the River Thames between 1884 and 2013

The world's longest record of river water quality (River Thames—130 years) provides a unique opportunity to understand fluvial dissolved organic carbon (DOC) concentrations dynamics. Understanding riverine DOC variability through long‐term studies is crucial to capture patterns and drivers influencing sources of DOC at scales relevant for decision making. The Thames basin (United Kingdom) has undergone massive land‐use change, as well as increased urbanisation and population during the period considered. We aimed to investigate the drivers of intra‐annual to interannual DOC variability, assess the variability due to natural and anthropogenic factors, and understand the causes for the increased DOC variability over the period. Two approaches were used to achieve these aims. The first method was singular spectrum analysis, which was used to reconstruct the major oscillatory modes of DOC, hydroclimatic variables, and atmospheric circulation patterns and to visualise the interaction between these variables. The second approach used was generalised additive modelling, which was used to investigate other non‐natural drivers of DOC variability. Our study shows that DOC variability increased by 80% over the data period, with the greatest increase occurring from the beginning of World War II onwards. The primary driver of the increase in DOC variability was the increase in the average value of fluvial DOC over the period of record, which was itself linked to the increase in basin population and diffuse DOC sources to the river due to land‐use and land‐management changes. Seasonal DOC variability was linked to streamflow and temperature. Our study allows to identify drivers of fluvial intra‐annual and interannual DOC variability and therefore empowers actions to reduce high DOC concentrations.     

NEWS

ABSTRACT

A stochastic model is proposed to describe flood-induced changes in cross sections of ephemeral streams with coarse bed-material. The model is based on the assumption that the real process can be described as a marked point process. The cumulative distribution functions of both the total change in a fixed interval of time and the maximum scour in the same period were examined. The model was run, using Monte Carlo techniques, with field data obtained from a small stream in southern Italy.     

Geochemistry and extractable Fe and Al in cold‐temperature soils of northwestern Siberia

The concentrations of major, minor and trace elements in three Cryosols from northwestern Siberia were analysed to determine profiles of geochemical uniformity, element mobility and the release and build‐up of extractable Fe and Al. The scope of this study involves weathering processes over all or part of the Lateglacial to the Holocene Epoch (<10 ka) in a cold environment. Iron and Al extracts are investigated to elicit information regarding profile age and palaeoclimate. ‘Free’ iron (Fe_d) relative to total Fe increases in the Ah + Bw horizons compared with the lower horizons, where oxidation is weaker. Low total Fe reflects reworked felsic deltaic and shallow marine deposits from the Permian to the early Tertiary, thereafter emplaced by episodic flooding of glacial meltwater from the Arctic Urals and/or the Kara Sea Ice Sheet. Organically complexed Al (Al_p), uniformly low in all soils, nevertheless shows trends indicating some downward movement, a rather unique occurrence in Arctic tundra soils. As indicated by the slow increase of oxihydrites, it may not be realistic to estimate the age of a profile by its physical characteristics. However, it appears possible to determine broad age ranges from the isotopic composition of water in soils. Copyright © 2009 John Wiley & Sons, Ltd.     

Collaborative geomatics and the Mushkegowuk Cree First Nations: Fostering adaptive capacity for community-based sub-arctic natural resource management

The remote First Nation (FN) communities of the Mushkegowuk Territory on the west coast of James Bay, Ontario, Canada are currently facing increased development pressures and the imposition of a government land use planning process. The land use planning process is mandated in the Far North Act (received Royal Assent on September 23, 2010). There is a need for capacity enhancement for community-based natural resource planning and management in the Territory. A number of frameworks are emerging for addressing change brought on by resource development and building resilience to such change at the community level. Among these include the concept of adaptive capacity. In collaboration with FN community leaders, we explored the use of “collaborative geomatics” tools to foster adaptive capacity. Our action research suggests that collaborative geomatics technologies should enhance the Mushkegowuk First Nations’ adaptive capacity to address environmental and policy change by allowing them to collect and manage data collaboratively (e.g., traditional environmental knowledge, western science) to create opportunities for innovative community development, including natural resource development and management.     

Ediacaran terrane accretion within the Arabian–Nubian Shield

The Ad Dawadimi Terrane is an Ediacaran basin of the Arabian Nubian Shield (ANS), Saudi Arabia. This basin terrane is situated in the far eastern part of the ANS and represents the youngest accretion event of the exposed ANS. Therefore, the timing of events within the basin is key to understanding both the closure of the Mozambique Ocean and the amalgamation of Gondwana along the northern East African Orogen. Here we present U/Pb detrital zircon data for the Abt Formation, the principle basin sediments of the Ad Dawadimi Terrane, along with ⁴⁰Ar/³⁹Ar ages on muscovite and whole rock Sm/Nd data. These data indicate that deep-water deposition in the Abt Basin did not end until after ca. 620 Ma and that deformation and greenschist-facies metamorphism of the Abt Formation occurred at 620 ± 3 (2σ) Ma along an active margin. This is the youngest terrane amalgamation event reported so far in the Arabian–Nubian Shield, but we suggest even younger sutures lie further east beneath the Phanerozoic cover of eastern Saudi Arabia. Our results suggest that the Ediacaran basins of the eastern ANS were not part of the Huqf basin in Oman, which was instead part of a passive margin of Neoproterozoic India, separated from the active margin of Africa by the Mozambique Ocean that probably did not close until the late Ediacaran or early Cambrian.     

The Sensitivity of the Phanerozoic Inorganic Carbon System to the Onset of Pelagic Sedimentation

The onset of pelagic sedimentation attending the radiation of pelagic calcifiers during the Mesozoic was an important divide in Earth history, shifting the locus of significant carbonate sedimentation from the shallow shelf environments of the Paleozoic to the deep sea. This shift would have impacted the CO₂ cycle, given that decarbonation of subducted pelagic carbonate is an important return flux of CO₂ to the atmosphere. Coupled with the fact that the mean residence time of continental platform and basin sedimentary carbonate exceeds that of the oceanic crust, it thus becomes unclear whether carbon cycling would have operated on a substantially different footing prior to the pelagic transition. Here, we examine this uncertainty with sensitivity analyses of the timing of this transition using a coupled model of the Phanerozoic atmosphere, ocean, and shallow lithosphere. For purposes of comparison, we establish an age of 250 Ma (i.e., after the Permo-Triassic extinctions) as the earliest opportunity for deposition of extensive biogenic pelagic carbonate on the deep seafloor, an age that predates known occurrences of pelagic calcifiers (and intact seafloor). Although an approximate boundary, we do show that attempts to shift this datum either significantly earlier or later in time produce model results that are inconsistent with observed trends in the mass–age distribution of the rock record and with accepted trends in seawater composition as constrained by proxy data. Significantly, we also conclude that regardless of the timing of the onset of biogenic pelagic carbonate sedimentation, a carbon sink involving seawater-derived dissolved inorganic carbon played a critical role in carbon cycling, particularly in the Paleozoic. This CaCO₃ sink may have been wholly abiogenic, involving calcium derived either directly from seawater (thus manifest as a direct seafloor deposit), or alternatively from basalt–seawater reactions (represented by precipitation of CaCO₃ in veins and fissures within the basalt). Despite the uncertainty in the source and magnitude of this abiogenic CaCO₃ flux, it is likely a basic and permanent feature of global carbon cycling. Subduction of this CaCO₃ would have acted as a basic return circuit for atmospheric CO₂ even in the absence of biogenically derived pelagic carbonate sedimentation. Lastly, model calculations of the ratio of dissolved calcium to carbonate ion (Ca²⁺/CO₃ ^2?) show this quantity underwent significant secular evolution over the Phanerozoic. As there is increasing recognition of this ratio’s role in CaCO₃ growth and dissolution reactions, this evolution, together with progressive increases in nutrient availability and saturation state, may have created a tipping point ultimately conducive to the appearance of pelagic calcifiers in the Mesozoic.     

Potential microbial bioinvasions via ships' ballast water, sediment, and biofilm

A prominent vector of aquatic invasive species to coastal regions is the discharge of water, sediments, and biofilm from ships' ballast-water tanks. During eight years of studying ships arriving to the lower Chesapeake Bay, we developed an understanding of the mechanisms by which invasive microorganisms might arrive to the region via ships. Within a given ship, habitats included ballast water, unpumpable water and sediment (collectively known as residuals), and biofilms formed on internal surfaces of ballast-water tanks. We sampled 69 vessels arriving from foreign and domestic ports, largely from Western Europe, the Mediterranean region, and the US East and Gulf coasts. All habitats contained bacteria and viruses. By extrapolating the measured concentration of a microbial metric to the estimated volume of ballast water, biofilm, or residual sediment and water within an average vessel, we calculated the potential total number of microorganisms contained by each habitat, thus creating a hierarchy of risk of delivery. The estimated concentration of microorganisms was greatest in ballast water>sediment and water residuals>biofilms. From these results, it is clear microorganisms may be transported within ships in a variety of ways. Using temperature tolerance as a measure of survivability and the temperature difference between ballast-water samples and the water into which the ballast water was discharged, we estimated 56% of microorganisms could survive in the lower Bay. Extrapolated delivery and survival of microorganisms to the Port of Hampton Roads in lower Chesapeake Bay shows on the order of 10(20) microorganisms (6.8 x 10(19) viruses and 3.9 x 10(18) bacteria cells) are discharged annually to the region.     

Trends in groundwater levels in wells in the active management areas of Arizona, USA

In 1980, the Arizona legislature passed the Groundwater Management Act (GMA), creating the active management areas (AMAs) to protect shared groundwater resources and to control severe overdrafts occurring in many parts of the state. With the 30-year anniversary of the GMA approaching, this article addresses the question: Have there been notable changes in the trends in observed groundwater levels in the AMAs from before enactment of the GMA until present? New tools developed for the US Geological Survey’s National Water Availability and Use Pilot Program are used to analyze and present trends in observed groundwater level data. Trends in groundwater levels in the AMAs were investigated for 10-year time periods from 1970 through 1999 and an 9-year period from 2000–2008. Results indicate that the number of wells with rising trends in water levels increased and the number of wells with falling trends in water levels decreased during the early decades after passage of the GMA in the most-populated Phoenix and heavily agricultural Pinal AMAs. However, these trends in water levels are reversed during the 1995–2004 time period. The value of trend analyses would be improved by consistent groundwater-level monitoring in both developed and undeveloped areas of the region.     

Time series analysis of long‐term river dissolved organic carbon records

Two long records of dissolved organic carbon (DOC) concentrations in river water were examined by a detailed time series analysis in order to shed light on the mechanisms generating observed increases in DOC concentrations across the UK. The records date back as far as 1962 and come from catchments 589 and 818 km² in area. The DOC records were compared with others taken simultaneously for flow, pH, alkalinity, air temperature and rainfall, and in one of the catchments also for turbidity and conductivity. All records were examined by the seasonal Kendall test; frequency distributions of daily DOC measurements were examined; annual cycles were calculated, Autoregressive and impulse functions were derived for DOC against flow records. The time series analysis shows that: (i) DOC trends cannot be readily explained by trends in flow, pH, alkalinity, turbidity or conductivity; (ii) there is a significant increase in carbon flux from these catchments; (iii) maximum and minimum components of the annual distribution of daily readings both show increases in DOC, implying that DOC flux is increasing for differing hydrological pathways; (iv) increases in DOC concentrations coincide with increases in temperature, though the biggest increases in temperature are in the winter months when such increases might be expected to have less effect on DOC production; (v) change in trend, and therefore flux, was observed to occur after a severe drought in 1976. The study suggests that there are real, significant increases in carbon loss from upland peat catchments and that climate is a major driver, especially a severe drought. Severe drought triggering changes in the DOC flux might be attributed to enzymic latch mechanisms. Copyright © 2004 John Wiley & Sons, Ltd.