The Mississippi River, the longest in North America, is really two rivers geophysically. The volume is less, the slope steeper, the velocity greater, and the channel straighter in its upper portion than in its lower portion. Below the mouth of the Ohio River, the Mississippi meanders through a continental depression that it has slowly filled with sediment over many millennia. Some limnologists and hydrologists consider the transitional middle portion of the Mississippi, where the waters of its two greatest tributaries, the Missouri and Ohio rivers, join it, to comprise a third river, in terms of its behavioral patterns and stream and floodplain ecologies.
The Mississippi River humans have known, with its two or three distinct sections, is a relatively recent formation. The lower Mississippi only settled into its current formation following the last ice age and the dissipation of water released by receding glaciers. Much of the current river delta is newer still, having taken shape over the last three to five hundred years.
Within the lower section of the Mississippi are two subsections, the meander zone and the delta. Below Cape Girardeau, Missouri, the river passes through Crowley’s Ridge and enters the wide and flat alluvial plain. Here the river meanders in great loops, often doubling back on itself, forming cut offs that, if abandoned by the river, forming lakes. Until modern times, most of the plain, approximately 35,000 square miles, comprised a vast and rich—rich in terms of biomass production—ecological wetland sustained by annual Mississippi River floods that brought not just water, but fertile sediment—topsoil—gathered from across much of the continent. People thrived in the Mississippi River meander zone. Some of the most sophisticated indigenous cultures of North America emerged here. Between Natchez, Mississippi, and Baton Rouge, Louisiana, at Old River Control, the Mississippi begins to fork into distributary channels, the largest of which is the Atchafalaya River. The Mississippi River delta begins here, formed of river sediment accrued upon the continental shelf. In the delta the land is wetter, the ground water table is shallower. Closer to the sea, the water becomes brackish and patterns of river sediment distribution are shaped by ocean tides and waves. The delta is frequently buffeted by hurricanes.
Over the last century and a half people have transformed the lower Mississippi River, principally through the construction of levees and drainage canals that have effectively disconnected the river from the floodplain. The intention has been to dry the land adjacent to the river, to make it useful for agriculture and urban development. However, an unintended effect of flood control and wetland drainage has been to interfere with the flood-pulse process that sustained the lower valley ecology, and with the process of sediment distribution that built the delta and much of the Louisiana coastline. The seriousness of the delta’s deterioration has become especially apparent since Hurricane Katrina, and has moved conservation groups to action. They are pushing politicians and engineers to reconsider their approach to Mississippi River management.
Margarete Kalin, William N. Wheeler, Michael P. Sudbury, and Bryn Harris
The first treatise on mining and extractive metallurgy, published by Georgius Agricola in 1556, was also the first to highlight the destructive environmental side effects of mining and metals extraction, namely dead fish and poisoned water. These effects, unfortunately, are still with us. Since 1556, mining methods, knowledge of metal extraction, and chemical and microbial processes leading to the environmental deterioration have grown tremendously. Man’s insatiable appetite for metals and energy has resulted in mines vastly larger than those envisioned in 1556, compounding the deterioration. The annual amount of mined ore and waste rock is estimated to be 20 billion tons, covering 1,000 km2. The industry also annually consumes 80 km3 of freshwater, which becomes contaminated.
Since metals are essential in modern society, cost-effective, sustainable remediation measures need to be developed. Engineered covers and dams enclose wastes and slow the weathering process, but, with time, become permeable. Neutralization of acid mine drainage produces metal-laden sludges that, in time, release the metals again. These measures are stopgaps at best, and are not sustainable. Focus should be on inhibiting or reducing the weathering rate, recycling, and curtailing water usage. The extraction of only the principal economic mineral or metal generally drives the economics, with scant attention being paid to other potential commodities contained in the deposit. Technology exists for recovering more valuable products and enhancing the project economics, resulting in a reduction of wastes and water consumption of up to 80% compared to “conventional processing.”
Implementation of such improvements requires a drastic change, a paradigm shift, in the way that the industry approaches metals extraction. Combining new extraction approaches, more efficient water usage, and ecological engineering methods to deal with wastes will increase the sustainability of the industry and reduce the pressure on water and land resources.
From an ecological perspective, waste rock and tailings need to be thought of as primitive ecosystems. These habitats are populated by heat-, acid- and saline-loving microbes (extremophiles). Ecological engineering utilizes geomicrobiological, physical, and chemical processes to change the mineral surface to encourage biofilm growth (the microbial growth form) within wastes by enhancing the growth of oxygen-consuming microbes. This reduces oxygen available for oxidation, leading to improved drainage quality. At the water–sediment interface, microbes assist in the neutralization of acid water (Acid Reduction Using Microbiology). To remove metals from the waste water column, indigenous biota are promoted (Biological Polishing) with inorganic particulate matter as flocculation agents. This ecological approach generates organic matter, which upon death settles with the adsorbed metals to the sediment. Once the metals reach the deeper, reducing zones of the sediments, microbial biomineralization processes convert the metals to relatively stable secondary minerals, forming biogenic ores for future generations.
The mining industry has developed and thrived in an age when resources, space, and water appeared limitless. With the widely accepted rise of the Anthropocene global land and water shortages, the mining industry must become more sustainable. Not only is a paradigm shift in thinking needed, but also the will to implement such a shift is required for the future of the industry.
Archis R. Ambulkar
Since the industrial revolution, societies across the globe have observed significant urbanization and population growth. Newer technologies, industries, and manufacturing plants have evolved over the period to develop sophisticated infrastructures and amenities for mankind. To achieve this, communities have utilized and exploited natural resources, resulting in sustained environmental degradation and pollution. Among various adverse ecological effects, nutrient contamination in water is posing serious problems for the water bodies worldwide.
Nitrogen and phosphorus are the basic constituents for the growth and reproduction of living organisms and occur naturally in the soil, air, and water. However, human activities are affecting their natural cycles and causing excessive dumping into the surface and groundwater systems. Higher concentrations of nitrogen and phosphorus-based nutrients in water resources lead to eutrophication, reduction in sunlight, lower dissolved oxygen levels, changing rates of plant growth, reproduction patterns, and overall deterioration of water quality. Economically, this pollution can impact the fishing industry, recreational businesses, property values, and tourism. Also, using nutrient-polluted lakes or rivers as potable water sources may result in excess nitrates in drinking water, production of disinfection by-products, and associated health effects.
Nutrients contamination in water commonly originates from point and non-point sources. Point sources are the specific discharge locations, like wastewater treatment plants (WWTP), industries, and municipal waste systems; whereas, non-point sources are discrete dischargers, like agricultural lands and storm water runoffs. Compared to non-point sources, point sources are easier to identify, regulate, and treat. WWTPs receive sewage from domestic, business, and industrial settings. With growing pollution concerns, nutrients removal and recovery at treatment plants is gaining significant attention. Newer chemical and biological nutrient removal processes are emerging to treat wastewater. Nitrogen removal mainly involves nitrification-denitrification processes; whereas, phosphorus removal includes biological uptake, chemical precipitation, or filtration. In regards to non-point sources, authorities are encouraging best management practices to control pollution loads to waterways.
Governments are opting for novel strategies like source nutrient reduction schemes, bioremediation processes, stringent effluent limits, and nutrient trading programs. Source nutrient reduction strategies such as discouraging or banning use of phosphorus-rich detergents and selective chemicals, industrial pretreatment programs, and stormwater management programs can be effective by reducing nutrient loads to WWTPs. Bioremediation techniques such as riparian areas, natural and constructed wetlands, and treatment ponds can capture nutrients from agricultural lands or sewage treatment plant effluents. Nutrient trading programs allow purchase/sale of equivalent environmental credits between point and non-point nutrient dischargers to manage overall nutrient discharges in watersheds at lower costs.
Nutrient pollution impacts are quite evident and documented in many parts of the world. Governments and environmental organizations are undertaking several waterways remediation projects to improve water quality and restore aquatic ecosystems. Shrinking freshwater reserves and rising water demands are compelling communities to make efficient use of the available water resources. With smarter choices and useful strategies, nutrient pollution in the water can be contained to a reasonable extent. As responsible members of the community, it is important for us to understand this key environmental issue as well as to learn the current and future needs to alleviate this problem.