Estuarine and coastal connectivity of an estuarine-dependent fishery species,Pomadasys commersonnii (Haemulidae)

Understanding the level of connectivity between estuarine and coastal waters is essential for appropriate management of estuarine-associated taxa. Most studies have focused on the role of a single estuary, while limited research exists on the importance of multiple estuaries to individuals of estuarine-associated species. This study used acoustic telemetry to assess the usage of multiple estuaries and coastal waters by the estuarine-dependent spotted grunter Pomadasys commersonnii. Twenty-six adult fish were tagged with acoustic transmitters in the Kariega and Bushmans estuaries, South Africa, and their movements along a 300-km stretch of Indian Ocean coastline were monitored for up to 17 months. Tagged individuals spent most of their time in the estuary where they were tagged (55% and 85% for fish tagged in the two estuaries, respectively), followed by time in the sea (30% and 15%) and in other estuaries (15% and <1%). The mean durations of sea trips for fish tagged in the Kariega Estuary or Bushmans Estuary, respectively, were 25 days (range 3–55) and 12 days (range 2–22). Of the fish that went to sea, 93% from the Kariega Estuary and 60% from the Bushmans Estuary visited other estuaries. Most visits were undertaken to the Swartkops, Bushmans and Kowie estuaries, although the longest durations were spent in the Sundays Estuary. Individuals moved to estuaries up to 130 km away. The total distance travelled between estuaries by an individual during the study was ～529 km, with means of 201 and 184 km, respectively, for fish tagged in the Kariega and Bushmans estuaries. Despite covering large distances between estuaries, individuals often returned to their tagging estuary. Residency in their tagging estuary, combined with frequent visits to a neighbouring estuary, highlights the importance of estuarine habitats for this popular fish species, even after reaching maturity.     

A Review of “The Middle East Today: Political,Geographical and Cultural Perspectives”

The tremendous changes in China's development philosophy and regional economies during the last two decades have carved out selectively new locations of development across the nation. While politicians heatedly debate the acceptable levels of regional inequality, most scholarly studies focus on broad aggregate trends of inequality among provinces and groups of provinces, and pay little attention to identifying and conceptualizing sources and major agents of spatial change. This paper aims at revealing detailed spatial ramifications of the reforms, and at understanding the impacts of the state, local agents, and foreign investors on regional development. To this effect, we conduct a disaggregated and empirical study of Jiangsu, a coastal province experiencing dramatic economic and spatial restructuring. We show that local agents which favor rural industrial enterprises accelerated new growth in selected rural areas, in contrast to slower growth of older cities and state-owned enterprises, resulting in a net decline of intercounty inequality. But the coalescence of state policy, local agents, and foreign investment has widened the historical gap between northern and southern Jiangsu, and is likely to accelerate intercounty inequality in the future. Our study demonstrates the utility of the “developments from above, below and outside” framework for analyzing key forces of regional growth in socialist transitional economies.     

Transient bacterial contamination of the dual-porosity aquifer at Walkerton,Ontario, Canada

Contamination of the Paleozoic carbonate aquifer at Walkerton (Ontario, Canada) by pathogenic bacteria following heavy rain in May 2000 resulted in 2,300 illnesses and seven deaths. Subsequent tracer testing showed that there was rapid groundwater flow in the aquifer, and also rapid exchange between the aquifer and the ground surface. Electrical conductivity (EC) profiling during a 3-day pumping test showed that most flow was through bedding-plane fractures spaced about 10 m apart, that there were substantial contrasts in EC in the major fracture flows, and that there were rapid changes over time. Total coliform sampling revealed transient groundwater contamination, particularly after heavy rain and lasting up to a few days. These characteristics can be understood in terms of the dual-porosity nature of the aquifer. Most of the storage is in the matrix, but this can be considered to be static in the short term. Almost all transport is through the fracture network, which has rapid groundwater flow (～100 m/day) and rapid transmission of pressure pulses due to the high hydraulic diffusivity. Rapid recharge can occur through thin and/or fractured overburden and at spring sites where flow is reversed by pumping during episodes of surface flooding. These characteristics facilitated the ingress of surface-derived bacteria into the aquifer, and their rapid transport within the aquifer to pumping wells. Bacterial presence is common in carbonate aquifers, and this can be explained by the well-connected, large-aperture fracture networks in these dual-porosity aquifers, even though many, such as at Walkerton, lack karst landforms.     

How preferential flow delivers pre‐event groundwater rapidly to streams

Groundwater often accounts for a substantial fraction of flood hydrographs, but the processes responsible for this have been unclear. However, many aquifers have preferential flow and this explains how aquifers can be so responsive. In bedrock aquifers, weathering enhances the connectivity and apertures along the most efficient flow paths and hence enhances the permeability. This results in celerities and velocities of the preferential flow in these dual‐porosity aquifers that are two to three orders of magnitude higher than if the aquifers behaved as single‐porosity media. The celerities have been determined from artificial and natural flood pulses, from tidal lags, and from pumping tests. Preferential‐flow velocities have been calculated from tests using applied tracers. Celerities in bedrock aquifers are typically one to two orders of magnitude faster than velocities. The ubiquitous preferential flow in aquifers provides an additional explanation, besides groundwater ridging, for the rapid release of groundwater to streams during storm events.     

Estimating Effective Porosity in Bedrock Aquifers

Flow in many bedrock aquifers is through fracture networks. Point to point tracer tests using applied tracers provide a direct measure of time of travel and are most useful for determining effective porosity. Calculated values from these tests are typically between 10⁻⁴ and 10⁻² (0.01% to 1%), with these low values indicating preferential flow through fracture and channel networks. Tracer tests are not commonly used in site investigations, and specific yield is often used as a proxy for effective porosity. The most popular methods have used centrifuge measurements, water table fluctuations, pumping tests, and packer tests. Specific yield varies substantially with the testing method. No method is as reliable as tracer testing for providing estimates of effective porosity, but all methods provide complementary insights on aquifer structure. Temporal and spatial scaling effects suggest that bedrock aquifers have hierarchical structures, with a network of more permeable fractures and channels, which are connected to less permeable fractures and to the matrix. Consequences of the low effective porosities include groundwater velocities that often exceed 100 m/d and more frequent microbial contamination than in aquifers in unconsolidated sediments. The large uncertainty over the magnitude of effective porosity in bedrock aquifers makes it an important parameter to determine in studies where time of travel is of interest.     

High sulfate concentrations in limestone springs: An important factor in conduit initiation?

Major ion concentrations in 404 springs in carbonate strata were found to exhibit a wide range in sulfate values. Sulfate concentrations are often much larger than would be expected from the analysis of samples from surface outcrops. Springs in the Sierra Madre Oriental (Mexico), the Rocky Mountains Front Range (Canada), and the Peak District (England) show similarities in sulfate concentration and in spatial distribution. Springs with high sulfate concentrations are found close to base level and are thermal. Springs with low sulfate concentration are found at higher elevations above base level and are not thermal. There is a direct relationship between sulfate concentration and spring temperature, and an inverse relationship with discharge. The results from the three areas described support a model of local and regional flow patterns, with deep regional flow providing the warm sulfate-rich water. The initial fracture porosity development in these aquifers may owe as much to the removal of sulfur minerals as to the removal of carbonate minerals. High sulfate values are frequently found in carbonate aquifers, so this model may be of widespread applicability.