**1. Introduction**

The kingdom of Lesotho is a small landlocked country in South Africa with a population of about 1.8 million [1] and occupies a total land area of 30,350 km2 [2] and has four distinct

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

agro-ecological zones (AEZ) based on the geology and climate (**Table 1**) [3] and has 10 districts (**Figure 1**).

Wetlands are among the Earth's most productive ecosystems. The significance of wetlands lie in their roles in the hydrological cycle, for flood and biomass production, as refuge for wildlife, biogeochemical functions, as nutrient and pollution filters for water quality improvement among others [4]. Globally, large percentage of these lands have been lost due to drainage and land clearance as consequence of agricultural, urban and industrial development activities [5–8]. According to Barbier et al., [9], the features of wetlands system can be grouped into *components, attributes* and *functions*. The *components* are the biotic and non-biotic features such as soil, water, plants and animals, while the *attributes* relate to the variability and diversity of these components e.g. diversity of species. However, the interactions between the components are expressions of the *functions* of the system such as nutrient cycling, water flow/exchange dynamics between the atmosphere (rainfall), the surface water and the shallow groundwater system. However, influence of agricultural land-use activity and hydrological modifications (affecting a biotic factor) are said to affects the attributes and functions of wetlands ecosystem [12–15].

Agriculture and wetlands has not had a very harmonious relationship in the past and agricultural activities have been affecting ground and surface water quality adversely from both point and non-point sources [10–12]. In Lesotho, wetlands are called *mekhuabo,* which apart from serving as refuge for wildlife, are primarily utilize to sustain agricultural activities at the local communities. These ecosystems support more than 300,000 households through agriculture and livestock watering. The wetlands ranged from several square meters to several square kilometers and occur in all the AEZs [13–15]. They can be categorized under three broad categories: palustrine, lacustrine and riverine [13, 16]. The palustrine wetlands are the dominant type and these include mires (bogs and fens), most of which are found at high altitude, at valley heads and at the upper reaches of rivers [8–12]. The lacustrine on the other hand occupies land area of ≥0.41 ha and comprises of artificial impoundments for water supply and soil conservation works (e.g. Katse and Mohale dams). The riverine wetlands are found along the river systems and these are generally small and often localized. In the recent years, there have been threats to wetlands across all the four AEZs [3, 22]. Threats to wetlands in Lesotho are attributable to over grazing, livestock watering; weed infestation, agricultural runoff and eutrophication, land reclamation for agricultural uses, and sedimentation of wetland beds [16, 23].

Current indicators of wetland monitoring often examine nutrient loadings such as soil and water total phosphorus (TP) and total nitrogen (TN) concentrations, species composition, biomass and primary production. These indicators often show the changes that have taken place on the impacted systems [24–26], but these have the shortcoming of identifying early ecosystems disturbance. However, the need for early and timely identification of systems of ecosystems disturbance is critical these days [27, 28]. Stable isotopes of carbon and nitrogen in organic matter offers an alternative means to detect early signs of environmental changes in aquatic ecosystems [29–32]. The ratios of 13C/12C and 15N/14N (defined as δ13C and δ15N) has been used to provide insight into the sources, sinks and cycling of carbon and nitrogen in aquatic ecosystems as these biota interact with its physical and chemical environments [33–36]. This study aimed at comparing the characteristics of wetland soils in the Lowland and Mountains AEZ in terms of soil characteristics, and compare the isotopic signatures (δ13C and δ15N) in these wetlands thereby understand the responses and mechanisms controlling the isotope variation in these wetlands. The ultimate goal is to identify causes of mismanagement and suggests plausible management options for a sustained and continuous use of these fragile lands for ecosystems services and agriculture.

Isotopic Signatures (δ<sup>13</sup>C and δ15N) and Characteristics of Two Wetland Soils in Lesotho…

http://dx.doi.org/10.5772/intechopen.80568

15

**Figure 1.** Population and land area in 10 districts of Lesotho.

The study was conducted on two wetlands located separately in two AEZs of Lesotho namely the Mountains (Butha-Buthe) and the Lowlands (Ha-Matela) (**Figure 2**). Butha-Buthe:

**2. Methods**


**Table 1.** Agro-ecological characteristics of Lesotho§ . Isotopic Signatures (δ<sup>13</sup>C and δ15N) and Characteristics of Two Wetland Soils in Lesotho… http://dx.doi.org/10.5772/intechopen.80568 15

**Figure 1.** Population and land area in 10 districts of Lesotho.

Current indicators of wetland monitoring often examine nutrient loadings such as soil and water total phosphorus (TP) and total nitrogen (TN) concentrations, species composition, biomass and primary production. These indicators often show the changes that have taken place on the impacted systems [24–26], but these have the shortcoming of identifying early ecosystems disturbance. However, the need for early and timely identification of systems of ecosystems disturbance is critical these days [27, 28]. Stable isotopes of carbon and nitrogen in organic matter offers an alternative means to detect early signs of environmental changes in aquatic ecosystems [29–32]. The ratios of 13C/12C and 15N/14N (defined as δ13C and δ15N) has been used to provide insight into the sources, sinks and cycling of carbon and nitrogen in aquatic ecosystems as these biota interact with its physical and chemical environments [33–36]. This study aimed at comparing the characteristics of wetland soils in the Lowland and Mountains AEZ in terms of soil characteristics, and compare the isotopic signatures (δ13C and δ15N) in these wetlands thereby understand the responses and mechanisms controlling the isotope variation in these wetlands. The ultimate goal is to identify causes of mismanagement and suggests plausible management options for a sustained and continuous use of these fragile lands for ecosystems services and agriculture.

#### **2. Methods**

agro-ecological zones (AEZ) based on the geology and climate (**Table 1**) [3] and has 10 dis-

Wetlands are among the Earth's most productive ecosystems. The significance of wetlands lie in their roles in the hydrological cycle, for flood and biomass production, as refuge for wildlife, biogeochemical functions, as nutrient and pollution filters for water quality improvement among others [4]. Globally, large percentage of these lands have been lost due to drainage and land clearance as consequence of agricultural, urban and industrial development activities [5–8]. According to Barbier et al., [9], the features of wetlands system can be grouped into *components, attributes* and *functions*. The *components* are the biotic and non-biotic features such as soil, water, plants and animals, while the *attributes* relate to the variability and diversity of these components e.g. diversity of species. However, the interactions between the components are expressions of the *functions* of the system such as nutrient cycling, water flow/exchange dynamics between the atmosphere (rainfall), the surface water and the shallow groundwater system. However, influence of agricultural land-use activity and hydrological modifications (affecting a biotic factor) are said to affects the attributes and functions of wetlands ecosystem [12–15].

Agriculture and wetlands has not had a very harmonious relationship in the past and agricultural activities have been affecting ground and surface water quality adversely from both point and non-point sources [10–12]. In Lesotho, wetlands are called *mekhuabo,* which apart from serving as refuge for wildlife, are primarily utilize to sustain agricultural activities at the local communities. These ecosystems support more than 300,000 households through agriculture and livestock watering. The wetlands ranged from several square meters to several square kilometers and occur in all the AEZs [13–15]. They can be categorized under three broad categories: palustrine, lacustrine and riverine [13, 16]. The palustrine wetlands are the dominant type and these include mires (bogs and fens), most of which are found at high altitude, at valley heads and at the upper reaches of rivers [8–12]. The lacustrine on the other hand occupies land area of ≥0.41 ha and comprises of artificial impoundments for water supply and soil conservation works (e.g. Katse and Mohale dams). The riverine wetlands are found along the river systems and these are generally small and often localized. In the recent years, there have been threats to wetlands across all the four AEZs [3, 22]. Threats to wetlands in Lesotho are attributable to over grazing, livestock watering; weed infestation, agricultural runoff and eutrophication, land

reclamation for agricultural uses, and sedimentation of wetland beds [16, 23].

Lowland 5200 <1800 Flat to gentle 600–900 −11 to 38 Senqu river valley 2753 1000–2000 Steep sloping 450–600 −5 to 36 Foot-hills 4588 1800–2000 Steep rolling 900–1000 −8 to 30

.

gentle rolling valleys

**Topography Mean annual** 

**rainfall (mm)**

1000–1300 −8 to 30

**Mean annual temperature (°C)**

tricts (**Figure 1**).

14 Wetlands Management - Assessing Risk and Sustainable Solutions

**Agro-ecological** 

**Area (km2**

Source: State of the Environment in Lesotho [9, 10].

**Table 1.** Agro-ecological characteristics of Lesotho§

**) Altitude (m)**

Mountains 18,047 2000–3484 Very steep bare rock and

**zones**

§

The study was conducted on two wetlands located separately in two AEZs of Lesotho namely the Mountains (Butha-Buthe) and the Lowlands (Ha-Matela) (**Figure 2**). Butha-Buthe: The wetland in Butha-Buthe is a palustrine wetland [13] and it is situated in the Mountain AEZ. It is located at an altitude/elevation of between 3181 and 3202 m above sea level (asl) and at points Latitude 28° 53.821/Longitude 28° 47.993 E. The site falls within the Afroalpine Grassland zone characterized by grasses-*Festuca caprina, Merxmuellera disticha* and *Pentaschistis oreodoxa;* shrubs and woody plants—*Chrysocoma ciliate, Erica dominans* and *Euryops evansii;* and other flowering plants—*Kniphofia caulescens, Helichrysum trilineatum, Dierama robustum, Zaluzianskaya ovate* and *Dianthus basuticus var. grandiflorus* [13]. Ha Matela: Ha Matela wetland is a Riverine wetland situated in the Foothills AEZ at an elevation of 1820 m above sea level, at points; Latitude: −29°38.3333/Longitude: 27°76.6667. It is characterized as the Afromontane Grassland zone. Dominant grasses includes: *Themeda triandra, Festuca caprina, Merxmuellera macowanii* and *Eragrostis curvula;* trees and shrubs: *Salix mucronata, Rhus erosa, Rhus pyroides, Leucosidea sericea, Myrsine Africana, Rhoicissus tridentate, Buddleja loricata* and *Chrysocoma ciliate* and flowering plants: *Gladiolus (several species), Kniphofia (several species), Helichrysum (many species), Agapanthus campanulatus subsp. Patens, Dierama robustum, Euphorbia clavarioides* and *Aloe polyphyll*. The geology of Lesotho is called formation [37] with sedimentary and volcanic clastics. Wetlands in these two agro-ecological zones: the Mountains and Lowlands (**Table 1**) were characterized as low, medium or high impacted wetlands based on local (i) land-use characteristics and (ii) intensity of anthropogenic pressures such as mining, smelting and discharge of industrial pollutant into the wetlands [38]. According to [38], the low impacted wetlands has little (i.e. <5%) or no agricultural activity within 150 m of the wetland boundary. Secondly, wetlands that were classified as highly impacted had agricultural activities; within 10 m of wetland boundary (i.e. < 33% of the wetland area is impacted). The medium impacted wetlands had agricultural activities between 5 and 32% of the wetland boundary. Wetlands in the Lowlands AEZ (i.e. Ha-Matela) were classified as being highly impacted, while that in the Mountains (i.e. Butha Buthe) had little impacts after [38]. About 2000 m transects were chosen and divided into upper (US), middle (MS) and toe slope (TS). Profile pits (1.20 m) were dug to reveal the natural soil horizons. Samplings were made in triplicates using the natural soil horizons. Soil samples were placed inside labeled plastic bags and shipped to the laboratory. Soils collected were analyzed after the standard methods:pH water (1:2 soil-water ratio) and pH-KCl (1:1 soil-water ratio), particle size analysis [39], total N [40] and available P (Bray-1-P)

Isotopic Signatures (δ<sup>13</sup>C and δ15N) and Characteristics of Two Wetland Soils in Lesotho…

C‐pool = *d* × *BD* × *organic carbon* (1)

(pH 7) and these were determined atomic absorption spectrophotometer (Perkin Elmer, 2007 AAS model WinLab) and flame photometers. Plant samples for isotopic signatures (i.e. δ13C and δ15N) in these wetlands were randomly collected in duplicates from the US, MS and TS sections of the toposequence/topography across years (2008–2010). These were labeled, airdried, and shipped to the Soil and Water Management and Crop Nutrition Laboratory, of the International Atomic Energy Agency (IAEA), Seibersdorf, Austria. The results are reported in standard δ notation as δ13C, δ15N, %C and %N values in reference to the international stan-

±2‰ for both δ13C and δ15N based on repeated analyses of laboratory standards. All data collected were subjected to analysis of variance (ANOVA) using the general linear model procedure (PROC GLM) of Statistical Analysis Systems (SAS) [44]. Means were separated

Generally, most of the wetlands across all agro-ecological zones of Lesotho are either used for livestock watering, grazing and agriculture and drinking water. In a related study on comparative assessments of wetlands in West and Southern Africa, it was found that most of the rural population used the wetlands largely for grazing and watering (**Figure 3**). It is evident from this result that approximately, 21% respectively of the population considered wetlands being important for irrigation and livestock grazing and watering. Similar observations were made by researchers from Southern Africa [45, 46], Taznania [47] and Kenya [45]. These authors found that wetlands constituted an important area of the livelihoods of the rural people. Hence, one of the major constraints to the sustainable use of wetlands in Lesotho and Africa in general is the lack of information on the diverse benefits that can be obtained from wetlands if properly managed. Hence, this information is needed by the government

A close observation of the soil physico-chemical properties of these wetlands is shown in **Table 2**. Results showed that the particle size distribution (i.e. texture) of the wetland soils at Butha Buthe was dominated by sand size texture compared to that at Ha-Matela. At the latter site, the particle size distribution had almost equal proportions of sand, silt and clay sized particles (**Table 2**). Both wetland soils generally had acidic soil pH (i.e. 4.69–5.44),

), d: soil layer thickness (m), BD: bulk density (kg m−<sup>3</sup>

). The base cations (Ca, Mg, Na and K) were by extracting soils with 1 N NH4

), organic car-

respectively. Analytical precision was

http://dx.doi.org/10.5772/intechopen.80568

OAc

17

[41], the organic carbon (OC) [42], and the SOC pool [43] and the equation:

dards Vienna Pee Dee Belemnite (V-PDB) and air N2

planners, natural resource managers and local communities.

using Duncan multiple range test (DMRT) at 5%.

**3. Results and discussion**

where C-pool (kgC m−<sup>2</sup>

bon (g g−<sup>1</sup>

**Figure 2.** The location of Lesotho within South Africa and its four agro-ecological zones.

to reveal the natural soil horizons. Samplings were made in triplicates using the natural soil horizons. Soil samples were placed inside labeled plastic bags and shipped to the laboratory. Soils collected were analyzed after the standard methods:pH water (1:2 soil-water ratio) and pH-KCl (1:1 soil-water ratio), particle size analysis [39], total N [40] and available P (Bray-1-P) [41], the organic carbon (OC) [42], and the SOC pool [43] and the equation:

$$\mathbf{C}\text{-pool} = d \times BD \times \text{organic\\_carbon} \tag{1}$$

where C-pool (kgC m−<sup>2</sup> ), d: soil layer thickness (m), BD: bulk density (kg m−<sup>3</sup> ), organic carbon (g g−<sup>1</sup> ). The base cations (Ca, Mg, Na and K) were by extracting soils with 1 N NH4 OAc (pH 7) and these were determined atomic absorption spectrophotometer (Perkin Elmer, 2007 AAS model WinLab) and flame photometers. Plant samples for isotopic signatures (i.e. δ13C and δ15N) in these wetlands were randomly collected in duplicates from the US, MS and TS sections of the toposequence/topography across years (2008–2010). These were labeled, airdried, and shipped to the Soil and Water Management and Crop Nutrition Laboratory, of the International Atomic Energy Agency (IAEA), Seibersdorf, Austria. The results are reported in standard δ notation as δ13C, δ15N, %C and %N values in reference to the international standards Vienna Pee Dee Belemnite (V-PDB) and air N2 respectively. Analytical precision was ±2‰ for both δ13C and δ15N based on repeated analyses of laboratory standards. All data collected were subjected to analysis of variance (ANOVA) using the general linear model procedure (PROC GLM) of Statistical Analysis Systems (SAS) [44]. Means were separated using Duncan multiple range test (DMRT) at 5%.
