**3.1 Large-scale African systems**

 Table Mountain Group (TMG) aquifer is a regional fractured-rock aquifer located in South Africa where the climate changes with elevation. The aquifer is a major source of water supply for agricultural and urban water requirements in the Western and Eastern Cape Provinces of South Africa [4]. Where the shale layers are not present, groundwater recharge can move deep into the transmissive sedimentary bedrock.

 **Figure 1** shows a schematic illustration of groundwater recharge and discharge areas and linkages of interaction between surface water and groundwater resources in the TMG aquifer [5]. Groundwater recharge mainly occurs in the higher elevation mountainous terrain areas, while natural discharge occurs in lower elevation valleys and foothills. Nevertheless, shallow groundwater occurs in the alluvial deposits, but downward movement is constrained by shale. The shallow groundwater has a shorter residence time and is not influenced by the more thermally connected mountain recharged water. This water is critical for plant and aquatic life, but during drought conditions, the shallow groundwater can be strained.

The main pathways of natural discharges from the TMG aquifer include 11 thermally heated springs and numerous cold spring discharges up through the quaternary and alluvial sediments providing baseflow to streams and reservoirs, wetlands, and seepage to the ocean [4].

 Groundwater discharges naturally and through man-made abstraction via wells. Groundwater is used for portable urban water supply and a variety of agricultural activities. The groundwater is a driving force which sustains human health and regional economy. Natural groundwater discharges from the TMG aquifer contribute to surface water resources in two major ways: firstly as contributions to the flow regime of mountain and foothill streams and rivers and secondly as groundwater contributions to wetlands and other aquatic ecosystems inclusive of marine discharges [4–6]. These natural discharges which take place in different ecotones and scales, as influenced by the subsurface heterogeneity, have an important role for nourishing and sustaining the plant and aquatic life systems in different ways.

#### **Figure 1.**

*A schematic illustration of the main groundwater recharge and discharge areas and linkages of interaction between surface water and groundwater resources in the TMG aquifer [5]. Source: [5].* 

Plants and fish adapt to the temperature and mineral content of the discharging groundwater. As shown in **Figure 1**, protecting the deep groundwater recharge areas is foundational to sustain human, plant, and animal health.

The Stampriet Transboundary Aquifer System (STAS) is shared between Namibia and Botswana, South Africa (**Figure 2**). The largest portions of the aquifer occur in Namibia's arid region which extends to Western Botswana and a small part of South Africa's Northern Cape Province. Auob and Nossob ephemeral rivers constitute the major surface water resources. The groundwater system is composed mainly of the unconfined Kalahari aquifer units overlying the Auob and Nossob confined sandstone aquifers [7].

Research has shown that most of the recharge occurs in the northwestern portion of the watershed in Namibia (**Figure 2**). The recharge typically occurs over a large diffuse area through the unconfined Kalahari formation. Water then preferentially recharges the confined aquifer systems where hydraulic heads and aquifer permeability converge. Several studies strongly suggest that sinkholes and bedrock faults act as the main pathways for preferential recharging of confined aquifers [8–10].

Natural groundwater discharge from the aquifer mainly occurs through evapotranspiration. Groundwater from the aquifer systems evapotranspires due to the aridity of the region. The Auob and Nossob rivers are ephemeral and lack consistent groundwater discharge; only a minimum contribution of groundwater discharge occurs through baseflow into the rivers. Nevertheless, evapotranspiration is also an important process to maintain/sustain the vegetative ecological balance. Given this reality, managers should not expect a robust healthy aquatic life.

Groundwater discharge from the transboundary aquifer also serves basic human needs for drinking and domestic use. Groundwater from the shared aquifer also supports a wide range of industries contributing economic growth and job creation.

**Figure 2.**  *Stampriet Transboundary Aquifer System and boreholes tapping from the aquifer [7].* 

*Sustainability of Human, Plant, and Aquatic Life: A Theoretical Discussion from Recharge… DOI: http://dx.doi.org/10.5772/intechopen.86171* 

**Figure 3** shows the relative percentage of land use for each river system [7]. While the scale of groundwater use is different in the three countries, groundwater discharge through abstractions appears to be sustainable.

### **3.2 North American outwash sandplains: wildlife and irrigated row crops**

The Anoka Sand Plain in Minnesota, USA (**Figure 4a**), and the Central Sands region of Wisconsin (**Figure 5**) are formed by rapid glacial melting which allowed meltwater to carry fine sediment south toward the Mississippi River; however, coarse-grain sediment was dropped out quickly to form large flat areas composed mostly of sand with gravel.

 Because dense compacted till was laid down by ice advances from Canada, infiltrating water can fill up the surficial sand and gravel aquifer but not move laterally unless a stream, lake, or wetland exists. Stream gradients in these regions are flat because the landscape is flat. In low-lying terrain, the groundwater manifests itself as large wetland complexes, whereas higher ground contains oak-prairie savannahs and crops. Some of these areas are protected by federal and state wildlife legislation [12], but most of the land is in some form of agricultural management. Because the soil has a high sand content, summer evapotranspiration can quickly dry up the upper topsoil, such that only deep-rooted plants survive the warm summer temperatures. High-value crops, such as potato and other vegetable crops, require irrigation to optimize plant vigor and specialty crop quality. In other locations, drainage via ditches is required to prevent crop loss. Some wetlands have been drained to grow grass, known as sod. Because sod is a high-value crop, pumps and lift stations are needed to prevent crop loss due to saturation. Because outwash regions are very flat, groundwater moves slowly unless an artificial gradient is created by ditches and pumps. There is an ongoing battle between nature and human development; the subdevelopment of homes, streets, parking lots, and shopping malls leads to urban runoff and stress upon the plant and animal (wildlife) ecological equilibrium.

 In the Central Sands region, intensive agricultural production has led to elevated nitrate-nitrogen concentrations which have threatened domestic drinking water users [14]. Aquatic life does not thrive well in flat channel gradients and sandy substrate; the flat terrain does not allow an adequate cold-water fishery, even though water temperatures in some channels are controlled by groundwater. Nevertheless, amphibian, mammal, and bird wildlife are abundant in wildland areas. Without governmental protection, these areas are at risk of losing their biodiversity [15].

### **3.3 Incipient karst: non-laminar groundwater flow**

Well-developed karst features are present in several parts of the world, most notably Croatia in Europe and Kentucky, USA. Incipient karst differs from developed karst because solution enlargement of fractures has not created caves. The thickness

**Figure 3.** 

*Groundwater use and abstraction per aquifer type in the Stampriet Transboundary Aquifer System. Source: [7].* 

#### **Figure 4.**

*(a) Illustration of the boundary of the Anoka Sand Plain highlighted in central Minnesota—darken area with a border. (b) Karst areas southeast of the Anoka Sand Plain in Minnesota [11]. Source: Environmental Trust Fund.* 

 of soil cover somewhat defines the boundary between incipient and developed karst (**Figure 4b**). Developed karst is dominated by sinkholes, underground cave streams, and point-source springs. Incipient or immature karst aquifers can have rapid water movement but may not have a landscape dotted with sinkholes and springs where cave streams resurge. Soil pipes are present, but they open and close quickly depending on cohesive soil bridging over bedrock. Subsurface erosion occurs through rock fractures in both carbonate and sandstone rock if the overlying soil is dominated by silt. The silty soil will bridge above a cavity until the soil-bearing strength is exceeded or triggered by changes in soil moisture or land use. The lack of abundant sinkholes makes land use development challenging because short of ground-penetrating radar or other geophysical measurement, there is no way to be certain a structure will not be swallowed by catastrophic collapse at some future date [16].

*Sustainability of Human, Plant, and Aquatic Life: A Theoretical Discussion from Recharge… DOI: http://dx.doi.org/10.5772/intechopen.86171* 

**Figure 5.**  *Location of the Central Sands region in Wisconsin [13]. Source: WiDNR webpage.* 

 With a changing climate, the risk of weak carbonic acid water in contact with limestone/dolomite fractures may drive fracture-opening enlargement, increasing the uncertainty of making sustainable groundwater management decisions. If all fractures below the landscape have a similar size and connectivity, Darcy's law and laminar flow can be assumed and modeled; however, nature's enlargement processes are not uniform but chaotic. This chaos leads to highly unpredictable flow paths and pollutant transport in relatively short time scales: on the order of minutes-to-days compared to months-to-years for Darcian flow. Hydrocarbons, pesticides, nutrients, and bacteria have been observed to move from the surface/near surface into shallow domestic wells and spring-fed streams over short time scales [17]. Future groundwater management will require a field monitoring effort that is more rigorous than sand and gravel systems. Tracking water and solute movement will require a monitoring system like those used in urban watersheds where water movement responds quickly to new precipitation. The largely unknown factor is storage; sustainability will depend upon creating watershed storage to buffer adverse ecosystem service change.

### **3.4 Midwest US Corn Belt: shallow groundwater**

Midwestern states of the USA produce the largest amount of corn grain on the planet. To achieve the massive amount of grain production, the land must be intensively managed to optimize crop growth. Large equipment for planting and harvesting, state-of-the-art agronomic practices from seed, chemical inputs to the grain storage, and marketing drive the Midwestern US economy. The landscape was once a vast sea of deep-rooted prairie grass and wetlands which helped form black fertile carbon-rich soil. In many locations soil wetness created uncertainty in crop management. To address this problem, wide-scale ditch drainage began over 100 years ago to optimize plant growth in wetland environments. Today fewer ditches are dug, but the use of plastic corrugated and perforated pipe that is placed into the soil with laser accuracy is a booming business. This land use practice helps remove excess water in the upper meter of cohesive soil; typically, sandy soils do not use subsurface pipe to improve soil aeration. The cohesive soil acts like incipient karst allowing water in the soils to move rapidly into the pipe because of fractured soil structure. In some ways the subsurface pipe functions like an urban environment producing pipe flow that transfers water to streams and ditches during and after a rainfall event. This change in hydrologic connectivity has caused downstream channels to enlarge over time leading to unstable banks and beds. Further, the chemicals applied to farm fields can move downward into the pipe and cause eutrophication of downgradient surface water. Nitrate-nitrogen has increased with increased placement of pipe; this has, in turn, led to Gulf of Mexico hypoxia [18]. To find a sustainable solution to this problem, water managers will need to find ways to hold water back and treat polluted runoff. Building soil health, regulating pipe discharge, and using bioreactors and saturated buffers are tools to be examined to minimize sediment and nutrient problems to downstream waterbodies.
