Creek Mouth Research Articles

Dynamics of nitrogen genes in intertidal sediments of Darwin Harbour and their connection to N-biogeochemistry

Microbial mediated nitrogen (N) transformation is subject to multiple controlling factors such as prevailing physical and chemical conditions, and little is known about these processes in sediments of wet-dry tropical macrotidal systems such as Darwin Harbour in North Australia. To understand key transformations, we assessed the association between the relative abundance of nitrogen cycling genes with trophic status, sediment partition and benthic nitrogen fluxes in Darwin Harbour. We analysed nitrogen cycling gene abundance using a functional gene microarray and quantitative PCRs targeting the denitrification gene (nosZ) and archaeal ammonia oxidation (AOA.1). We found a significant negative correlation between archaeal ammonia oxidation and silicate flux (P = 0.004), an indicator for diatom and benthic microalgal activity. It is suggested that the degradation of the diatomaceous organic matter generates localised anoxic conditions and inhibition of nitrification. Abundance of the nosZ gene was negatively correlated with nutrient load. The lowest nosZ gene levels were in hyper-eutrophic tidal creeks with anoxic conditions and increased levels of sulphide limiting the coupling of nitrification-denitrification (P = 0.016). Significantly higher levels of nosZ genes were measured in the surface (top 2 cm) compared to bulk sediment (top 10 cm) and there was a positive association with di-nitrogen flux (N2) in surface (P = 0.024) but not bulk sediment. This suggests that denitrifiers are most active in surficial sediment at the sediment-water interface. Elevated levels of nosZ genes also occurred in the sediments of tidal creek mouths and mudflats with these depositional zones combining the diffuse and seaward supply of nitrogen and carbon supporting denitrifiers. N-cycle molecular assays using surface sediments show promise as a rapid monitoring technique for impact assessment and measuring ecosystem function. This is particularly pertinent for tropical macrotidal systems where systematic monitoring is sparse and in many cases challenged by climatic extremes and remoteness.

Hydrologic remobilisation of tephra‐fall deposits: A sedimentological analysis throughout fluvio‐lacustrine systems of North‐West Patagonia

AbstractThis paper explores the response to Holocene ash inundation in different sub‐environments of two fluvio‐lacustrine systems, Las Piedritas and Totoral, focussing on the processes of volcaniclastic remobilisation. Sediment cores and outcrops were used to recognise three deposit types, noting how some differ from lahars, through sedimentological and stratigraphic analysis: (1) thick, laterally discontinuous, pumice‐dominated deposits occur overlying alluvial plain and lower terrace surfaces across both watersheds; (2) chaotic, extremely poorly sorted and matrix‐supported beds composed of both epiclastic and pyroclastic material occur as two conspicuous deposits at Las Piedritas outcrops, in a low‐gradient confined channel setting; and (3) layers with an exclusively pyroclastic composition and no flow sedimentary structures or fragment roundness were found draping each of the two chaotic intervals and intercalating with the background sediment in Las Piedritas prodelta. Thick pumice packages capping the floodplains resulted from the overflow of streams carrying a floating pumice load. Due to its positive buoyancy, the pumice is transported as a slowly moving overlying mantle without mixing with the streamflow. The disorganised pattern and poor sorting of the matrix‐rich polymictic beds are consistent with laminar, gravity‐driven, high‐concentration flows. They constitute secondary lahars, originating upstream from large run‐off processes that reworked a pyroclastic substrate. The lack of reworking features in the vitric‐rich units identified in the lake core retrieved from Las Piedritas prodelta, as well as the continuous and widespread occurrences of those interbedded in upstream outcrops, indicate an airfall origin. No reworked tephra unit is recognised in the prodelta sediment record, although various deposits from the hydrologic remobilisation of airfall tephra are found along the subaerial portion of both watersheds. Apparently, large amounts of flotation‐remobilised tephra were retained on the delta plain, while another considerable fraction would have been carried away from the creek mouth under the influence of dominant regional winds.

Концентрация и эмиссия метана и сероводорода в озере Баскунчак, ручье балки Улан-Благ и дегазирующих источниках подземных вод в весенний период

For the first time, the distribution of methane in the brine and bottom sediments of Lake Baskunchak, as well as its tributary, the Ulan-Blag stream, in the beam of which the discharge of ascending degassing groundwater sources takes place, was studied. In addition to CH4, concentrations of total hydrogen sulfide (ΣH2S), Eh and pH values, humidity and density were determined in various horizons (up to 35 cm) of stream sediments. Concentrations of CH4, major ions and pH values were determined in the brine of the lake and stream; experimental measurements of CH4 emission by the chamber method were carried out on one of the debit fields where degassing sources are discharged. Brine mineralization in Lake Baskunchak is 312 g/dm3, which is 2.1 times more than in the Ulan-Blag stream; the water class in the stream and lake is chloride, the sodium group, type II and III, respectively. The fluxes of CH4 into the atmosphere from the surface of the studied degassing source vary in the range of 1.97–2.07 mg/(m2 h). In the brine of degassing sources, a high concentration of CH4 (up to 215 μl/dm3) is recorded, which is 1-2 orders of magnitude higher than in the brine of the lake. Low concentrations of CH4 in the brine of the lake are due to its insignificant flow from bottom sediments into the water due to the presence of a salt crust that prevents gas emission, as well as due to its small concentrations in the upper layers of sediments (0.01 μg/g). Low concentrations of CH4, despite the reducing conditions, are also characteristic of the sediments of the mouth of the Ulan-Blag creek (0.04–0.32 μg/g), which, at high concentrations of ΣH2S in them (0.06–1.32 mg/g), is probably caused by the suppression of methanogenesis in the sediments by sulfate reduction. In general, the distribution of CH4 and ΣH2S along the vertical of deposits is quite synchronous (r = 0.64) and correlates with the distribution of Eh values.

Geophysical surveys and satellite imaging for the evaluation of near‐surface terrain dynamic – A case study on Grand Portage, MN, USA

AbstractFlooding, erosion and increases in the water level in Lake Superior have contributed to changes in the stem location and width of the Grand Portage Creek. Those events threaten parts of the Grand Portage National Monument, a historically significant site on the North Shore of Lake Superior, Minnesota. We performed geophysical surveys to investigate these dynamic effects. We studied the near‐surface geological deposits, the mechanisms associated with creek stem dynamics and sediment transport, as well as deposition along the lakeshore in Grand Portage Bay. We deployed ground‐penetrating radar (GPR), sub‐bottom profiler, side scan sonar, Geoprobe coring and Van Veen grab samplers and evaluated time‐lapse satellite images to assess the interaction of the Grand Portage Creek with the Grand Portage Bay. The onshore GPR surveys next to the national monument, the creek and the shoreline showed the presence of a complex deposition with eroded ground surfaces and sediment layers across the creek valley. Results from the offshore geophysical campaigns and the interpretations of satellite images also document a heterogeneous deposition sequence environment with fine‐grained sediment deposits present south and southwest of the creek mouth. In addition, we documented an exposed boulder bed towards the east of the creek mouth that was exposed by the current and wave‐driven erosion process in the Grand Portage Bay. Time‐lapse satellite images and hydraulic current velocity simulations validate these observations and provide insight into how anthropogenic activities and natural events interact and might contribute to the long‐term stability of a site of historical and cultural importance.

High‐frequency and long‐term observations of eDNA from imperiled salmonids in a coastal stream: Temporal dynamics, relationships with environmental factors, and comparisons with conventional observations

AbstractA greater understanding of eDNA behavior in the environment is needed before it can be employed for ecosystem monitoring applications. The objectives of this study were to use autonomous sampling to conduct long‐term, high‐frequency monitoring of the eDNA of native salmonid species in a Californian coastal stream, describe temporal variation of eDNA on multiple scales and identify environmental factors that drive this variation, and evaluate the ability of the eDNA datasets to detect rare species and represent organismal abundance. Using high‐throughput autonomous environmental sample processors (ESPs) and qPCR, we enumerated eDNA concentrations from 674 water samples collected at subdaily intervals over 360 days at a single site. We detected eDNA from two imperiled salmonids (coho salmon Oncorhynchus kisutch and steelhead/rainbow trout O. mykiss) in most samples; O. kisutch eDNA was generally in lower concentration and more variable than O. mykiss eDNA. High‐frequency (i.e., subdaily and daily) variability in salmonid eDNA concentrations showed occasional patchiness (i.e., large differences between consecutive samples), while seasonal differences were observed consistent with the ecology of the species at this site. Salmonid eDNA concentrations were significantly associated with creek discharge, photoperiod, and whether the creek mouth was open or closed by a seasonal sandbar. The release of hatchery‐origin O. kisutch parr into the stream was associated with a significant increase in eDNA concentration for the remainder of the study. We compared eDNA signals with fish abundance data collected from traps located at the site. Fish were detected more often by eDNA than from trapping. Significant positive associations between fish abundance and eDNA concentrations were observed for O. mykiss; however, no such associations were observed for O. kisutch. This study adds to our knowledge on the occurrence and behavior of fish eDNA in lotic systems and informs future biomonitoring efforts using automated sampling technology.

Analysis of shoreline changes along the coast of Tiruvallur district, Tamil Nadu, India

Shoreline change is considered as one of the most dynamic process, which was mapped along the coast of Tiruvallur district by using topographic maps of 1976 and multi-temporal satellite images. The satellite images were pertaining to 1988, 1991, 2006, 2010, 2013 and 2016 which were used to extract the shorelines. It is important to map and monitor the HTL (High Tide line) at frequent time interval as it considered as shoreline, which was demarcated by using visual interpretation technique from satellite images and topographic maps. Followed by this, an overlay analysis was performed to calculate areas of erosion and accretion in the study area. The results revealed that the coast of Tiruvallur district lost 603 ha and gained 630 ha due to erosion and accretion respectively. It was confirmed after the ground truth survey carried out in the study area. The high accretion of 178 ha was found nearby Pulicat Lake and low accretion of 19 ha seen between Pulicat lake to Kattupali port. The high erosion area was found along the Pulicat lake, Kattupali and Ennore ports, and Ennore creek mouth and south of Ennore such as Periya Kuppam, Chinna Kuppam, Kasi Koil Kuppam, and Thyagarajapuram. It may be concluded that the main causes of coastal erosion and accretion in the study area are anthropogenic and natural factors, which alter the coastal environment.

Fibropapillomatosis infection in a population of green turtles at Watamu Bay, Kenya

Anthropogenic stressors from onshore and offshore activities can act as driving factors of disease for a wide range of marine organisms. Green turtles (Chelonia mydas) are prominently afflicted with a tumour-causing disease known as fibropapillomatosis (FP) caused by the chelonid alphaherpesvirus ChHV5. Previous studies indicate that pathways of FP transmission may be genetic (vertical transmission) or linked to causal factors in a turtle’s environment (horizontal transmission). In this paper patterns of FP prevalence were examined in 10,896 records of green turtles caught or found stranded around Watamu Bay, Kenya, between 2003 – 2020. Findings were focused on locational and seasonal factors that may potentially influence infection. The findings show that FP prevalence varies significantly on an annual basis. Location significantly influenced infection prevalence, with prevalence higher in open ocean sites than sites located within the creek. Infection prevalence was highest at sites around the creek mouth and north of the creek mouth, with both regions exhibiting disparate annual patterns of infection. This paper is the first to examine long-term trends of FP prevalence in-depth in this region and has implications for the health of turtles and marine biota found along the Kenyan coast, and potentially within the wider Western Indian Ocean region. The findings emphasize the need to distinguish the infection pathways of causative agents via: i) further examination of the links between infection and environmental and/or biont community factors; and ii) the collection of data pertinent to the genetic diversity of green turtles and associated ChHV5 viral strains occurring in the Western Indian Ocean.

Analysis of shoreline changes along the coast of Tiruvallur district, Tamil Nadu, India

Shore line change is considered as one of the most dynamic processes, which were mapped along the coast of Tiruvallur district by using topographic maps of 1976 and multi-temporal satellite images. The satellite images pertaining to 1988, 1991, 2006, 2010, 2013 and 2016 were used to extract the shorelines. It is important to map and monitor the HTL (High Tide Line) at frequent time intervals as the shoreline was demarcated by using visual interpretation technique from satellite images and topographic maps. Followed by this, an overlay analysis was performed to calculate areas of erosion and accretion in the study area. The results revealed that the coast of Tiruvallur district lost 603 ha and gained 630 ha due to erosion and accretion respectively. It was confirmed after the ground truth survey carried out in the study area. The high accretion of 178 ha was found nearby Pulicat Lake and low accretion of 19 ha was seen between Pulicat Lake and Kattupali Port. The high erosion area was found along the Pulicat Lake, Kattupali and Ennore ports, and Ennore creek mouth and southern Ennore such as Periya Kuppam, Chinna Kuppam, Kasi Koil Kuppam, and Thyagarajapuram. It may be concluded that the coastal erosion and accretion in the study area were mainly caused by anthropogenic and natural factors, which altered the coastal environment.

Seasonal influence of water quality on the assemblage and diversity of phytoplankton along Dubai Creek, Arabian Gulf

The research aims to find out the seasonal variation in phytoplankton diversity, composition and their abundance in response to various environment parameters. Seasonal variation in the phytoplankton community associated with various biological and water quality parameters (Temperature, Salinity, Dissolved Oxygen (DO), Nitrate (NO3-N), Phosphate (PO4-P), Chlorophyll-a, Phaeophytin and Carotenoids) were studied along 10 sampling stations of the Dubai Creek during January–December 2018. One-way ANOVA (p< 0.005) and correlation coefficient between the phytoplankton abundance and the physico-chemical parameters revealed positive trends of phytoplankton composition. The phytoplankton species diversity varied from 55 (Sanctuary) to 95 (Creek mouth). A total of 110 species of phytoplankton were recorded in Dubai Creek, comprising of 76, 29, 3, 1 and 1 species of Bacillariophyceae, Dinophyceae, Cyanophyceae, Euglenophyceae and Ciliophora respectively. The annual mean variation in phytoplankton population were recorded between 744 (Hyatt Regency) to 31906 cells × 103 L−1 (STP outfall). Due to the morphology, hydrodynamic regime and polluted nature in the upper Creek presented an unique phenomenon where the phytoplankton species and density divided Dubai Creek into two (2) sections. The first section (downstream of the Dubai Creek) include the stretch from the Creek mouth to the Floating bridge stations with low population and high species diversity, whereas the other section (upstream of the Dubai Creek) cover stations from Al Gharhoud bridge up to the Sanctuary with dense population and low species diversity. The diversity index showed highest along downstream of Dubai Creek. A ‘k’ dominance plots for phytoplankton abundance between samples showed lower and higher steep curves along downstream (Creek mouth, Abra and Hyatt Regency) and upstream regions (Al Jaddaf, Sanctuary and STP outfall) of Dubai Creek. This could probably de due to the polluted and unpolluted conditions of the Creek. Bray–Curtis cluster analysis showed strong similarity (>60%) among upstream stations of Dubai Creek associated with polluted conditions, whereas an overlap of Creek mouth, Abra and Hyatt Regency on remaining stations showed unpolluted and healthy conditions of the phytoplankton in downstream stations. Canonical Correspondence Analysis revealed that Bacillariophyceae have a positive strong relationship with different environment variables between stations Abra, Hyatt Regency and Creek mouth, indicating influence of high flushing of the coastal waters on phytoplankton species and diversity. The study presents an outline of the seasonal dynamic relationship between phytoplankton structure and environmental conditions in the Dubai Creek.

Beach restoration improves habitat quality for American horseshoe crabs and shorebirds in the Delaware Bay, USA

Beach nourishment is commonly conducted to protect human infrastructure but rarely for the primary purpose of improving wildlife habitat. To improve horseshoe crab spawning and shorebird feeding habitat in the Delaware Bay, New Jersey (USA), we removed 2000 t of shoreline rubble and placed sand on 16 ha of degraded shoreline spanning 8 beaches. Horseshoe crab egg cluster abundance varied annually, seasonally and spatially. Beaches restored using sand with grain size fractions similar to native sand had horseshoe crab egg cluster abundances matching or exceeding those of high-quality reference beaches. Deeper sand with a higher coarse-grain fraction resulted in the highest egg cluster abundance across all sites and beaches, while finer-grained sand used on a subset of restored beaches was associated with lower egg cluster abundances. These patterns were also reflected in shallow egg availability for shorebirds, with egg cluster abundance correlating positively with shallow egg abundance. Over time, sand placed on beaches moved cross-shore and longshore, and overwashed into marshes. Longshore sand movement nourished adjacent beaches and ebb shoals at creek mouths. Such shoals attract spawning horseshoe crabs and have high densities of surface eggs available for shorebird feeding, but experience high attrition of egg clusters. This study demonstrates that investments in beach restoration provide important benefits for horseshoe crabs and shorebirds. Outcomes can be further improved by expanding project scope and integrating other coastal restoration strategies. Restoration will be critical for the conservation of coastal species as sea levels rise and current and past coastal management practices continue to degrade habitats.

Multi‐scale spatial dynamics of the Chesapeake Bay nettle, Chrysaora chesapeakei

AbstractUntangling organisms' multi‐scale spatial distributions is challenging due to their interactions with environments at multiple spatial and temporal scales. We deployed an Adaptive Resolution Imaging Sonar (ARIS) in a Chesapeake Bay sub‐estuary to investigate multi‐scale spatial distributions of the bay nettle (Chrysaora chesapeakei) in May–September of 2016 and 2017. Nettles were found to be dispersed in aggregations of multiple individuals. The average density of bay nettles in 2017 was higher than in 2016. Small aggregations (&lt;5 m) were persistent in both years but only contributed &lt;10% of total observed nettles. Large patches (&gt;30 m) contributed ~40% of the total observed nettles. Large patches were more common in creek habitat where nettle density was higher. Nettle density was found to hit a peak value once in 2016, while there were two density peaks in 2017. Different aggregation patterns were observed during the second peak period in 2017 in which the number of large patches increased dramatically. Within the surveyed waterscape, the spatial patterns were consistent over time with higher abundance in the source creek than in the river channel, which underscores that C. chesapeakei requires hard substrate in shallow creeks for its benthic polyp stage. Using the ratio between nettles in the creek and near creek mouth as a proxy for dispersal rate, more nettles were transported out of the creek in 2017 than in 2016. The increase in patch size and high dispersion rate in peak periods in 2017 suggests that individuals were moving out of the creek habitat as density increased. Results highlight the complex spatial structure of bay nettles, which has major impacts on density estimates and subsequently affects our understanding of jellyfish population dynamics and long‐term trends.

The Role of a Tidal Flat–Saltmarsh System as a Source–Sink of Mercury in a Contaminated Coastal Lagoon Environment (Northern Adriatic Sea)

The Marano and Grado Lagoon (northern Adriatic Sea, Italy) is contaminated mainly by mercury (Hg) of mining and industrial origin. This work aims to investigate the sedimentary records of Hg of a tidal flat–saltmarsh (TF–S) system and to understand the role played by tidal fluxes in terms of the transport, accumulation and release of Hg due to the periodic flow of the tide. The complex history of the sources of Hg in the area of the TF–S system has resulted in several fluctuations of Hg in sediments over time; due to its higher sedimentation rate (1.3 cm year−1) than the subtidal areas of the Grado lagoon, the outer area of the TF–S system is more active in terms of accumulation (from 56 to 81 mg m−2 year−1) than the inner area. Fluxes were estimated at the mouth of a principal tidal creek by combining discrete hourly tidal flow measurements with weighed measurements of dissolved (DHg) and particulate (PHg) mercury obtained via water sample collection. Mercury, mainly in particulate form, is drained by the tidal creek from the marsh during a tidal semi-cycle. The highest flux of PHg was recorded during ebb tide in July (1071 mg). The calculation of the quantitative flows of PHg and DHg highlighted a tendency for Hg to be exported from the TF–S to the lagoon channel during a tidal semi-cycle. However, the results obtained here for the Hg fluxes do not allow for the depiction of a constant positive or negative budget as that found in the literature for macro-scale budget calculations at lagoon tidal inlets. A possible explanation for there being no constant trend in the PHg and DHg budget is that our TF–S system is located in a lagoon area where previous findings reported accretion or a balance situation between erosion and sedimentation processes.

Geomorphology and Species Interactions Control Facilitation Cascades in a Salt Marsh Ecosystem.

Facilitation cascades are chains of positive interactions that occur as frequently as trophic cascades and are equally important drivers of ecosystem function, where they involve the overlap of primary and secondary, or dependent, habitat-forming foundation species [1]. Although it is well recognized that the size and configuration of secondary foundation species' patches are critical features modulating the ecological effects of facilitation cascades [2], the mechanisms governing their spatial distribution are often challenging to discern given that they operate across multiple spatial and temporal scales [1, 3]. We therefore combined regional surveys of southeastern US salt marsh geomorphology and invertebrate communities with a predator exclusion experiment to elucidate the drivers, both geomorphic and biotic, controlling the establishment, persistence, and ecosystem functioning impacts of a regionally abundant facilitation cascade involving habitat-forming marsh cordgrass and aggregations of ribbed mussels. We discovered a hierarchy of physical and biological factors predictably controlling the strength and self-organization of this facilitation cascade across creekshed, landscape, and patch scales. These results significantly enhance our capacity to spatially predict coastal ecosystem function across scales based on easily identifiable metrics of geomorphology that are mechanistically linked to ecological processes. Replication of this approach across vegetated coastal ecosystems has the potential to support management efforts by elucidating the multi-scale linkages between geomorphology and ecology that, in turn, define spatially explicit patterns in community assembly and ecosystem functioning.

Seasonal Toxicity Observed with Amphipods (Eohaustorius estuarius) at Paleta Creek, San Diego Bay, USA.

To assess potential impacts on receiving systems, associated with storm water contaminants, laboratory 10-d amphipod (Eohaustorius estuarius) survival toxicity tests were performed using intact sediment cores collected from Paleta Creek (San Diego Bay, CA, USA) on 5 occasions between 2015 and 2017. The approach included deposition-associated sediment particles collected from sediment traps placed at each of 4 locations during the 2015 to 2016 wet seasons. The bioassays demonstrated wet season toxicity, especially closest to the creek mouth, and greater mortality associated with particles deposited in the wet season compared with dry season samples. Grain size analysis of sediment trap material indicated coarser sediment at the mouth of the creek and finer sediment in the outer depositional areas. Contaminant concentrations of metals (Cd, Cu, Hg, Ni, Pb, and Zn) and organic compounds (polycyclic aromatic hydrocarbons [PAHs], polychlorinated biphenyls [PCBs], and pesticides) were quantified to assess possible causes of toxicity. Contaminant concentrations were determined in the top 5 cm of sediment and porewater (using passive samplers). Whereas metals, PAHs, and PCBs were rarely detected at sufficient concentrations to elicit a response, pyrethroid pesticides were highly correlated with amphipod toxicity. Summing individual pyrethroid constituents using a toxic unit approach suggested that toxicity to E. estuarius could be associated with pyrethroids. This unique test design allowed delineation of spatial and temporal differences in toxicity, suggesting that storm water discharge from Paleta Creek may be the source of seasonal toxicity. Environ Toxicol Chem 2019;39:229-239. © 2019 SETAC.

A septic waste index model to measure the impact of septic tanks on coastal water quality and coral reef communities in Rincon, Puerto Rico

The impact of fecal contamination of coastal waters and coral reefs is a major cause of concern in marine reserves in Puerto Rico. The measurement of the association between septic tank frequency in watersheds of creeks draining into these reserves and coastal water quality and coral reef condition is of importance in configuring pollution control policy. Fecal coliforms and enterococci assays were used to measure the density of fecal contaminants across the Tres Palmas Marine Reserve (TPMR) in Rincon, Puerto Rico. Inshore waters are intermittent creeks, receiving fecal pollution only from faulty septic tanks. Fecal indicators measurements showed higher densities near the southernmost creek mouth emptying into TPMR, a finding consistent with a larger amount of dwellings with septic tanks within this watershed (Vista Azul creek). A Septic Weight Index was constructed to analyze sewage impact from all watersheds draining into the marine reserve. Linear Regression analyses showed a significant association between these non-point source fecal pollution sources and both coastal water quality and impact on some parameters measuring the condition of Acropora palmata coral reef colonies.

Stable Isotopes and Bayesian Modeling Methods of Tracking Sources and Differentiating Bioavailable and Recalcitrant Phosphorus Pools in Suspended Particulate Matter

Understanding the sources of different phosphorus (P) pools and their bioavailability under imposed biogeochemical environments in a watershed is limited largely due to the lack of appropriate methods. In this research, phosphate oxygen isotope ratios and Bayesian modeling on fingerprinting elements were applied as two novel methods to identify sources and relative recalcitrancy of particulate P pools suspended in water in the continuum of sources from land to the mouth of a coastal estuary to the Chesapeake Bay. Comparative analyses of sizes, relative ratios, and oxygen isotope values of particulate P pools in the creek water suggested that the NaHCO3-P pool was bioavailable, whereas NaOH-P and HCl-P pools were recalcitrant during P transport along the creek. Agricultural field soil, streambank, and river bottom sediments were major sources of particulate P and their contributions varied significantly at the headwater and downstream regions of the creek. Bayesian modeling based on fingerprinting elements suggested that tides played a major role in forming particulate matter from estuarine sources at the creek mouth region and importing it upstream. These findings provide new insights into the origin and fate of particulate P and the fidelity of isotope and fingerprinting methods in source tracking of P in tidally influenced watersheds.

The influence of neap–spring tidal variation and wave energy on sediment flux in salt marsh tidal creeks

AbstractSediment flux in marsh tidal creeks is commonly used to gauge sediment supply to marshes. We conducted a field investigation of temporal variability in sediment flux in tidal creeks in the accreting tidal marsh at China Camp State Park adjacent to northern San Francisco Bay. Suspended‐sediment concentration (SSC), velocity and depth were measured near the mouths of two tidal creeks during three 6‐ to 10‐week deployments: two in winter and one in summer. Currents, wave properties and SSC were measured in the adjacent shallows. All deployments spanned the largest spring tides of the season. Results show that tidally averaged suspended‐sediment flux (SSF) in the tidal creeks varied from slightly landward to strongly bayward with increasing tidal energy. SSF was negative (bayward) for tidal cycles with maximum water surface elevation above the marsh plain. Export during the largest spring tides dominated the cumulative SSF for each deployment. During ebb tides following the highest tides, velocities exceeded 1 m s−1 in the narrow tidal creeks, resulting in negative tidally averaged water flux, and mobilizing sediment from the creek banks or bed. Storm surge also produced negative SSF. Tidally averaged SSF was positive in wavy conditions with moderate tides. Spring tide sediment export at the creek mouth was about twice that at a station 130 m further up the tidal creek. The negative tidally averaged water flux near the creek mouth during spring tides indicates that in the lower marsh some of the water flooding directly across the bay–marsh interface drains through the tidal creeks, and suggests that this interface may be a pathway for sediment supply to the lower marsh as well. Copyright © 2018 John Wiley &amp; Sons, Ltd.

Assessment of sea water inundation along Daboo creek area in Indus Delta Region, Pakistan

Indus Deltaic Region (IDR) in Pakistan is an erosion vulnerable coast due to the high deep water wave energy. Livelihood of millions of people depends on the fisheries and mangrove forests in IDR. IDR consists of many creeks where Daboo is a major creek located at southeast of the largest city of Pakistan, Karachi. Unfortunately, there has been no detailed study to analyze the damages of sea water intrusion at a large temporal and spatial scale. Therefore, this study is designed to estimate the effects of sea water inundation based on changing sea water surface salinity and sea surface temperature (SST). Sea surface salinity and SST data from two different surveys in Daboo creek during 1986 and 2010 are analyzed to estimate the damages and extent of sea water intrusion. Mean salinity has increased 33.33% whereas mean SST decreased 13.79% from 1987 to 2010. Spatio-temporal analysis of creek area using LANDSAT 5 Thematic mapper (TM) data for the years 1987 and 2010 shows significant amount of erosion at macro scale. Creek area has increased approximately 9.93% (260.86 m2 per year) which is roughly equal to 60 extensive sized shrimp farms. Further Land Use Land Cover (LULC) analyses for years 2001 and 2014 using LANDSAT 7 Enhanced Thematic Mapper Plus (ETM+) has indicated 42.3% decrease in cultivated land. Wet mud flats have spread out at the inner mouth of creek with enormous increase of 123.3%. Significant sea water intrusion has increased the area of barren land by 37.9%. This also resulted in overall decrease of 6.7% in area covered by mangroves. Therefore, this study recorded a significant evidence of sea water intrusion in IDR that has caused serious damages to community living in the area, economical losses. Additionally, it has also changed the environment by reducing creek biological productivity as reported by earlier studies over other regions of the world.

Coastal wetlands, sea level, and the dimensions of geomorphic resilience

Geomorphic system resilience is often perceived as an intrinsic property of system structure and interactions but is also related to idiosyncratic place and history factors. The importance of geographical and historical circumstances makes it difficult to generate categorical statements about geomorphic resilience. However, network-based analyses of system structure can be used to determine the dynamical stability (=resilience) based on generally applicable relationships and to determine scenarios of stability or instability. These provide guidelines for assessing place and history factors to assess resilience. A model of coastal wetlands is analyzed, based on interactions among relative sea level, wetland surface elevation, hydroperiod, vegetation, and sedimentation. The system is generally (but not always) dynamically unstable and non-resilient. Because of gradients of environmental factors and patchy distributions of microtopography and vegetation, a coastal wetland landscape may have extensive local variations in stability/resilience and in the key relationships that trigger instabilities. This is illustrated by a case study where dynamically unstable fragmentation is found in two nearby coastal wetlands in North Carolina's Neuse River estuary—Otter Creek Mouth and Anderson Creek. Neither is keeping pace with relative sea level rise, and both show unstable state transitions within the wetland system; but locally stable relationships exist within the wetland systems.

Monitoring Re-Suspension and Transport of Dioxin Contaminated Sediment to Evaluate the Recovery of a Shallow Urban Creek Post Sediment Remediation

Pringle Creek, identified as the source of dioxin/furan (PCDD/F) contamination to a Lake Ontario harbour was remediated in 2008. Surface sediment collected in 2013 near the floodplain remediation was no longer contaminated (∑17PCDD\Fs ∑17PCDD\Fs 2900 pg/g dw). Nevertheless, sediment ∑17PCDD/F concentrations were lower in 2013 than pre-remediation suggesting that cleaner sediment was being deposited in the creek. Core data confirmed the decrease in sediment contamination through time since the most contaminated sediment was buried. Prior to the development of a remediation strategy for the harbour, the transport of bed-load and suspended sediment contaminated with PCDD/F was assessed. The challenge was the shallow water depth (0.6 m) throughout the creek thereby requiring non-standard sediment traps designed for this study. Suspended sediment collected in traps in 2014 showed residual contamination at the remediated site (∑17PCDD\Fs: 380 pg/g dw; TEQ (TEF fish) ∑17PCDD\Fs concentration for suspended sediment at the creek mouth was 2200 pg/g (SD 260 pg/g dw) indicating PCDD/F contributions to the harbour. However, congener patterns in bottom sediment and suspended sediment near the remediated site and extending about 100 m downstream were similar to background upstream patterns consistent with atmospheric deposition as the source rather than the historical source which indicated that floodplain remedial actions were successful.