Morphodynamics of the Manyema tidal delta at Kunduchi, Tanzania

The prevailing northward longshore drift of beach sand on the northern part of Msasani Bay, north of Dar es Salaam, is interrupted at Kunduchi by the tidal flushing of Manyema Creek, a mangrove ecosystem partially developed for salt production. Shoreline changes around the creek mouth in recent decades have eroded coastal land and destroyed buildings, prompting stakeholders to construct protective groynes and revetments. Sand is transported across the delta by the interaction of two forcing processes – currents of water flushing the creek in response to tidal variation; and (generally) currents generated by wind-driven waves according to the monsoon season. Study of the sand morphology of the creek and delta platform together with time-series satellite imagery has permitted demarcation of the respective sand transport pathways and of morphodynamic changes on the delta over the last decade. The sand transport regime has promoted erosion of the shore to the south of the creek mouth and has led to a spasmodic delivery of sand to beaches north of the channel. Attempts to stabilise the shore around the creek mouth are described and their effectiveness evalutated

From marine bands to hybrid flows: sedimentology of a Mississippian black shale

Organic‐rich mudstones have long been of interest as conventional and unconventional source rocks and are an important organic carbon sink. Yet the processes that deposited organic‐rich muds in epicontinental seaways are poorly understood, partly because few modern analogues exist. This study investigates the processes that transported and deposited sediment and organic matter through part of the Bowland Shale Formation, from the Mississippian Rheic–Tethys seaway. Field to micron‐scale sedimentological analysis reveals a heterogeneous succession of carbonate‐rich, siliceous, and siliciclastic, argillaceous muds. Deposition of these facies at basinal and slope locations was moderated by progradation of the nearby Pendle delta system, fourth‐order eustatic sea‐level fluctuation and localized block and basin tectonism. Marine transgressions deposited bioclastic ‘marine band’ (hemi)pelagic packages. These include abundant euhaline macrofaunal tests, and phosphatic concretions of organic matter and radiolarian tests interpreted as faecal pellets sourced from a productive water column. Lens‐rich (lenticular) mudstones, hybrid, debrite and turbidite beds successively overlie marine band packages and suggest reducing basin accommodation promoted sediment deposition via laminar and hybrid flows sourced from the basin margins. Mud lenses in lenticular mudstones lack organic linings and bioclasts and are equant in early‐cemented lenses and in plan‐view, and are largest and most abundant in mudstones overlying marine band packages. Thus, lenses likely represent partially consolidated mud clasts that were scoured and transported in bedload from the shelf or proximal slope, as a ‘shelf to basin’ conveyor, during periods of reduced basin accommodation. Candidate in situ microbial mats in strongly lenticular mudstones, and as rip‐up fragments in the down‐dip hybrid beds, suggest that these were potentially key biostabilizers of mud. Deltaic mud export was fast, despite the intrabasinal complexity, likely an order of magnitude higher than similar successions deposited in North America. Epicontinental basins remotely linked to delta systems were therefore capable of rapidly accumulating both sediment and organic matter

Beach sand supply and transport at Kunduchi, Tanzania, and Bamburi, Kenya

Beach-head erosion of sandy beach plains in eastern Africa threatens tourism-related infrastructure and the livelihoods of beach plain users. The nature and drivers of physical shoreline change at Kunduchi, near Dar es Salaam, and Bamburi, near Mombasa, are described with analyses of beach sand transport through the annual monsoon cycle and the provenance and sustainability of beach sand supply. Time-series records of wind-vectors at Dar es Salaam and Mombasa show similar averaged patterns. Because of the contrasting alignments of these coasts, the net wind-wave driven longshore transport at Kunduchi (NNW-trending) is north-northwestwards, while at Bamburi (NNE-trending) there is little net transport over the cycle. At Bamburi, the beaches are recharged reef/platform-derived calcium carbonate sand and siliciclastic sand discharged from the hinterland via tidal channels. At Kunduchi, recharge is mostly river-borne siliciclastic sand, but river sand mining threatens natural replenishment. At both sites eroding beach plain deposits contribute siliciclastic sand. Structural responses to maintain beaches protecting susceptible shores – mostly seawalls at Bamburi and groyne fields at Kunduchi – have high capital and maintenance costs, degrade the coastal amenity and may exacerbate erosion. At Kunduchi, beach maintenance is further jeopardised by unchecked illegal river sand mining

Review of agricultural pollution in the Caribbean with particular emphasis on small island developing states

Recent studies have attributed the degradation of coastal living resources in the Caribbean to the potential impacts of agricultural pollution. Physical features controlling the delivery, retention and dispersal of pollutants throughout the region are discussed. Information relating to four types of agricultural pollution is presented and assessed: soil erosion leading to siltation, nutrient enrichment, pesticide contamination and agro-industrial pollution. The results of this review have enabled gaps in knowledge to be identified. Areas prone to soil erosion and the reasons for their susceptibility are known. There is a paucity of baseline data on turbidity and on the concentration of nutrients and pesticides in the coastal zone. The increase in the use of agricultural fertilisers and pesticides over the last 20 years suggests a concomitant rise in their loads to coastal waters. Few studies have made direct links between agricultural pollution, reduction in coastal water quality or clarity, and the degradation of coastal living resources

Review of agricultural pollution in the Caribbean with particular emphasis on small island developing states

Recent studies have attributed the degradation of coastal living resources in the Caribbean to the potential impacts of agricultural pollution. Physical features controlling the delivery, retention and dispersal of pollutants throughout the region are discussed. Information relating to four types of agricultural pollution is presented and assessed: soil erosion leading to siltation, nutrient enrichment, pesticide contamination and agro-industrial pollution. The results of this review have enabled gaps in knowledge to be identified. Areas prone to soil erosion and the reasons for their susceptibility are known. There is a paucity of baseline data on turbidity and on the concentration of nutrients and pesticides in the coastal zone. The increase in the use of agricultural fertilisers and pesticides over the last 20 years suggests a concomitant rise in their loads to coastal waters. Few studies have made direct links between agricultural pollution, reduction in coastal water quality or clarity, and the degradation of coastal living resources

Environmental problems caused by gypsum karst and salt karst in Great Britain

In Great Britain, gypsum karst is widespread in the Late Permian (Zechstein) gypsum of north-eastern England. Here and offshore, a well-developed palacokarst with large breccia pipes was formed by dissolution of the underlying Permian gypsum. Farther south, around Ripon, the same rocks are still being dissolved, forming an actively evolving phreatic gypsum-maze cave system. This is indicated by the presence of numerous active subsidence hollows and sulphate-rich springs. In the English Midlands, gypsum karst is locally developed in the Triassic deposits south of Derby and Nottingham. Where gypsum is present, its fast rate of dissolution and the collapse of overlying strata lead to difficult civil-engineering and construction conditions; these can be further aggravated by water abstraction. Salt (halite) occurs within British Permian and Triassic strata, and has a long history of exploitation. The main salt fields are in central England and the coastal areas of northwest and northeast England. In central England, saline springs indicate that rapid, active dissolution occurs that can cause subsidence problems. In the past, subsidence was aggravated by shallow mining and the uncontrolled extraction of vast amounts of brine. This has now almost stopped, but there is a legacy of unstable buried salt karst, formed by both natural and induced dissolution. The buried salt karst occurs at depths ranging from about 40 m to 130 m; above these depths, the overlying strata are foundered and brecciated. In the salt areas, construction and development are hampered by both abandoned mines and by natural or induced brine runs, with their associated unstable ground