A Review of Water Quality Indices Used to Assess the Health Status of High Mountain Wetlands

The health status of wetlands depends to a large extent on the permanence and quality of water. However, natural and anthropogenic pressures on these ecosystems are transforming them and driving them to generate timely and reliable information. The aim of this study is to provide a review of water quality indices used to assess the health status of high mountain wetlands. To this end, an exhaustive search was initially carried out for studies with significant contributions to the knowledge of high mountain wetlands in Peru. In total, 90 articles on wetlands published in the last decade (2007-2017) were reviewed through bibliographic managers, of which 25% corresponded to wetland studies in Peru and of these only 6% to water quality in high Andean wetlands.


Introduction
Livelihoods in developing countries are highly dependent on intact and functioning wetlands.Permanency and water quality have been identified as factors that affect the structure and composition of biological communities [1]; as well as the services provided by these ecosystems (groundwater recharge, flood water retention, static baseflow contributions, biogeochemical processing, improved water quality and wildlife habitat) [2].However, these factors responsible for maintaining the integrity of aquatic ecosystems are strongly influenced by pop-ulation growth, urbanization, land-use change, hydrological-climatic changes and traditional practices [3] [4].
Studies on the overall extent of wetlands, especially in South Asia and South America, show that wetlands have declined by 6% in just 14 years (de 1993 a 2007) due to continued and disorderly urban growth [5].These changes have generated in recent decades the need to better assess and manage the cumulative effects of human interventions on wetlands [6] [7] [8] [9].The use of biological communities to assess the ecological status of water bodies has become a major component of water-related legislation worldwide [10] [11], as they provide a quantifiable response to various environmental disturbances [12].
High Andean wetlands are an integral part of the landscape as they provide habitat for a diversity of plants and animals.They also act as buffers for floods and erosion, and serve as key links in the global water and biogeochemical cycles [13].Although it is difficult to measure the state they are in, a healthy wetland must generally demonstrate good water quality and functioning [14].In other words, a healthy wetland should not show signs of stress related to substantial degradation or cumulative effects of minor degradation, and should be exempt from modifications that restrict the flow of water into or out of the wetland, or that alter seasonality patterns.
In particular, there is a need to address the value of the high Andean wetlands as a "sink" for many chemicals, including atmospheric carbon, and other key functions they perform.However, these high Andean water ecosystems are still the least studied and one of the most threatened ecosystems.The decline in water quality in these ecosystems comes mainly from inadequate management, although they play a fundamental role in human well-being and the global importance they have in maintaining ecological balance.In this regard, the aim of this study is to provide a review of the indices for assessing anthropogenic impact in water quality in high Andean wetlands.

Organization and Method of Study
The study is divided into five sections.In the first section, a summary of the current status of the high Andean wetlands is provided.The second section emphasizes anthropogenic pressures on water quality.The third section presents the physico-chemical or conventional index.In the fourth and fifth sections, the biotic and multicriterio indices are presented, respectively.For it, an exhaustive search was initially carried out for studies with significant contributions to knowledge of the high Andean wetlands.Then, and considering that the good health status of wetlands depends to a large extent on the permanence and quality of water, we proceeded to identify studies aimed at assessing the health status of these ecosystems and the indices that determine it.In total, 90 articles on wetlands published in the last decade (2007-2017) were reviewed through bibliographic managers, of which 25% corresponded to wetland studies in Peru and of these only 6% to water quality in high Andean wetlands (

Current Status of the High Andean Wetlands
The high Andean wetlands, located at an altitude of 3300 meters above sea level, are shallow water ecosystems associated with streams, rivers, lagoon edges, springs and thaw waters that harbor characteristic biological communities, have a permanent or temporary water regime and are considered fragile ecosystems under natural and anthropogenic pressure [30].
The historical data on the health status of the high Andean wetlands is rudimentary, as there is no real estimate of the area of wetlands in good conservation status and how many have been lost.Despite the efforts of the state entities with environmental competence to generate cartographic information on vegetation cover in Peru [31] and many researchers from the Andean region that have projected changes in precipitation and temperature behavior, hydrology and climatology studies in these ecosystems are scarce [32].This paucity of information makes it difficult to understand the potential impacts of anthropogenic activities and climate change (Figure 1).
Water pollution in the high Andean wetlands is a major threat to species with restricted geographic ranges and narrow ecological niches, plant and animal endemism in the eastern Andean slope: Challenges to conservation [33] [34] [35].
Also, water transfer works to the coast that increases the risk of loss of high Andean wetlands [36] [37].Consequently, as the wetland area is lost, key functions of these ecosystems are lost, among which stand out for their importance and global value: supporting biodiversity, improving water quality, reducing flooding and sequestering carbon.

Anthropogenic Impact on Water Quality
Inland aquatic ecosystems around the world are undergoing changes in quality, quantity and biodiversity due to pollution by different types of pollutants such as fertilizers, wastewater and heavy metals resulting from the development of anthropogenic activities [38].The increase in these activities is putting strong pressure on this resource and interfering with vital and legitimate uses of water at the local, regional or international level [39] [40].The overexploitation and pollution of water, as well as the degradation of aquatic ecosystems, are having a direct impact on the well-being of populations that depend on these ecosystems for their livelihoods.
The high Andean wetlands are ecosystems of great ecological value, with a rich fauna consisting of communities with a complex structure and high biological value.However, their special typology makes them fragile and vulnerable to environmental changes, especially those related to anthropogenic disturbances, which often involve irreversible degradation of their biota [41] [42].The vulnerability of these habitats is also evident in relation to the potential impacts of climate change.One of the predictable effects could be that some of these systems will change from permanent to seasonal and some will even disappear.As a result, the biodiversity of many of them will be reduced and their biogeochemical cycles altered [43].

Water Quality Indices
The constant battle to develop the most appropriate method for assessing water quality in aquatic systems has allowed indicators to be integrated into indices that reveal more accurate information regarding their state.Water quality indices aim at giving a single value to the water quality of a source reducing great amount of parameters into a simpler expression and enabling easy interpretation of monitoring data.Classically, physico-chemical indicators have been used to evaluate the entry, distribution and dispersion of chemical agents in the aquatic environment and their assimilation into living tissues [44].However, when pollutants enter sporadically these indicators are no longer of choice, as they are only an instantaneous reflection of the environmental condition.In contrast, indicators based on biological communities allow for temporal integration and reveal a current or past effect of anthropogenic disturbances.Thus, water pollution control has become a key element of effective policies to prevent, control and reduce the content of dangerous substances, nutrients and other water pollutants from point sources in aquatic ecosystems.[45], which, unlike the WQI-NSF, which is oriented towards waters to be used for human consumption, considers five uses of water (human consumption, agriculture, fishing and aquatic, industrial and recreational life) [46].Other indices proposed in the last decade are: WQI of raw water for public supply-IAP of Brazil; calculated from the WQI of NSF and the toxic substance index-ISTO (CETESB 2006), the Universal Water Quality Index U-WQI consisting of 11 physico-chemical indicators and a bacteriological [47] based on European Union Directives, and the Drinking Water Quality Index-DWQI developed to assess the global situation of water collection sources [48] (Table 2).

National Sanitation Foundation's Water Quality Index (NSF-WQI)
Brown et al. [49] developed a water quality index similar in structure to the Horton index but much more rigorously in the selection of indicators, developing a common scale and assigning weights for which Delphic exercises were developed.This effort was supported by the National Sanitation Foundation (NSF).
For this reason, the Brown index is also known as NSF-WQI [50].However, in the course of using the index, it was found that the arithmetic or additive formulation, while easy to understand and calculate, lacked sensitivity in terms of the effect that a single bad parameter value would have on the WQI.This led to Brown et al. [51] to propose a variation of NSF-WQI, a multiplicative formulation.

Dinius' Second Index
A multiplicative water-quality index was developed by Dinius with liberal use of Delphi in decision making [52].The index included 12 pollutants e dissolved oxygen, BOD 5 , coliform count, E. coli, pH, alkalinity, hardness, chloride, specific conductivity, temperature, colour and nitrate e for six water uses e public water supply, recreation, fish, shellfish, agriculture and industry.The sub index functions CCMEWQI 100 1.732 were worked out as summarized in Table 3.

A Universal Water-Quality Index (U-WQI)
Boyacioglu, took into consideration the water-quality standards set by the Council of European Communities [53], the Turkish water pollution control regulations and other scientific information to select 12 water-quality parameters as the most representative for drinking water quality.They set three classes of water e representing "excellent", "acceptable" and "polluted" categories (Table 4).

The Canadian Council of Ministers of Environment Water Quality Index (CCME-WQI)
The CCME-WQI is an adaptation of the BCWQI, which consists of three factors, each of which has been scaled between 0 and 100.In the CCME-WQI, the values of the three variance measures of the selected objectives for water quality are combined to create a vector in an imaginary space of "objective exceedance".
In the index, "objectives" refer to water quality guidelines across Canada or site-specific water quality objectives [54].The length of the vector is then scaled to range between 0 and 100, and subtracted from 100 to produce an index which is 0 (or close to 0) for very poor water quality, and close to 100 for excellent water quality.The CCME-WQI consists of three factors as shown in Figure 2.
Factor 1 (F 1 ) Scope: This factor is called scope because it assesses the extent of the noncompliance of water-quality guideline over the period of interest. 1

Number of failed variables 100
Total number of variables where variables indicate those water-quality parameters with objectives which were tested during the time period for the index calculation.
Factor 3 (F 3 ) Amplitude: It represents the amount by which the failed test values do not meet their objectives, and is calculated in three steps: 1) The number of times by which an individual concentration is greater than (or less than, when the objective is a minimum) the objective is termed an "excursion" and is expressed as follows.When the test value must not exceed the objective.

Failed Test Value Excursion 1 Objective
Figure 2. Three-dimensional representation of the water quality index by adding three factors (F 1 , F 2 and F 3 ) as vectors [55].
For the cases in which the test value must not fall below the objective: 2) The total extent by which individual tests fail to comply is calculated by summing the excursions of individual tests from their objectives and dividing by the total number of tests (those which do and do not meet their objectives).This variable, referred to as the normalised sum of excursions, or nse, is calculated as: 3) F 3 is then calculated by an asymptotic function that scales the normalised sum of the excursions from objectives (nse) to yield a range between 0 and 100: The CCME-WQI is finally calculated as: ( ) ( ) ( ) CCM-EWQI 100 1.732 The factor of 1.732 arises because each of the three individual index factors can range as high as 100.This means that the vector length can reach 100 100 100 30000 173.2 + + = = as a maximum.Division by 1.732 brings the vector length down to 100 as a maximum.It may be seen that the CCME-WQI is closely related to the BCWQI which, in turn, has been found to be extremely sensitive to sampling design and on the chosen water-quality objective [56].

Biotic Indices
The concept of the Water Quality Index (WQI) was introduced in its rudimentary form more than a century ago when the presence or absence of certain organisms in a water source was used as an indicator of the stressful forces of human activities [57] [58].The first WQI in history was therefore a "biotic" index (Figure 3).
Biotic indices are more "expressive" and revealing of ecological health.In biotic indices, each taxon from a particular group of organisms is assigned a sensitivity weighting, or a "score", based on the tolerance or sensitivity of that taxon to particular pollutants [59] [60].The scores of all the individual taxa sampled at a site are summed and/or averaged to provide a value by which the ecological health of the biotic community, hence the health of the water body, can be gauged [61].Some biotic indices include abundance estimates in the scoring system [62].

Biotic Indices Based on Macroinvertebrates
There are several advantages in using benthic macroinvertebrates in bioassess-ment [63] [64].
Benthic macroinvertebrates are largely nonmobile, ubiquitous and relatively abundant inhabitants of both lotic and lentic habitats.There are often many species within a community with varying sensitivities to stresses and relatively quick reaction times, resulting in a spectrum of graded, recognizable responses to environmental perturbations [65].Also, responses to different types of pollution have been established for many common species.Macroinvertebrates have life cycles that are long enough for temporal changes caused by perturbations to be detected, but short enough to enable the observation of decolonization patterns following perturbation [66].They are relatively easy and inexpensive to collect, particularly if qualitative sampling is undertaken, and are well suited to the experiments required for biomonitoring.Studies have shown that the issue of variability in the types of habitats of macroinvertebrates within a water body can be easily resolved by pooling of samples [67] [68].

Biological Monitoring Working Party (BMWP) Score System
In this system, which was introduced in 1978 and modified in 1980 and 1983, all major aquatic habitat types are sampled with a pond net of 90 mm mesh size for a total of 3 min and taxa are identified in the field.The score values for all the predefined invertebrate families present in the sample for a site are summed to give the Total BMWP Score [69] [70] [71] [72].The value ranges from less than 16 for severely polluted waters to more than 120 where very clean water indicator families can be found (Table 5).There are many global adaptations of this index, including the one adapted by Custodio and Amésquita (BMWP-PeA) [73] to evaluate high Andean lotic systems, which considers values ranging from less than 15 to more than 120.The most difficult challenge in index development is selecting and combining metrics in a manner that is complex enough to capture the dynamics of essential ecological processes but not so complex that its meaning is obscured [79].

Multimetric Indices Based on Environmental Indicators
Without a sound and obvious ecological foundation, an index will not be policy relevant and therefore difficult to use in the DPSIR systems.Once developed, such indices fall into three classes [80], based upon their complexity, information content and method of metric combination: 1) Univariate individual-species data, or community structure measures.
2) Multimetric indices, combining several measures of community response to stress into a single index.
3) Multivariate methods describing the assemblage pattern.

Multimetric Indices Based on Macroinvertebrates
Next to fish, most IBIs have revolved round macroinvertebrates [81]- [86].Macroinvertebrates are generally sedentary and it is relatively easier and simpler to sample them than fish.However, there are several disadvantages in using macroinvertebrates for IBIs.Firstly individuals are often variably distributed, causing problems in sampling and metric development [87] [88].Secondly, a great deal of time and effort is associated with taxonomic identification prior to metric development [89].Thirdly, high temporal variability of macroinvertebrates is a major factor limiting their use in ecological health indices [90].Ephemoptera, Plecoptera and Trichoptera (EPT) have been commonly used in the metrics of macroinvertebrate-based IBIs.Percent Oligochaetes is another commonly used metric.Whereas the relative abundance of EPT decreases in disturbed water bodies, that of Oligochaetes, which is a pollution-tolerant taxon, increases.

Conclusions
The evaluation of water quality using physico-chemical parameters represents a monitoring approach based on stressors, whiles the same objective, when ad-
These indices are based on the integration of different physico-chemical indicators to provide a global vision of water quality.The values of physico-chemical indices can vary from 0 (very poor quality) to 100 (excellent quality).At a global level, different indices have been developed, including the WQI of the National Sanitation Foundation of the United States (WQI-NSF), which has been validated and adapted in different countries, and the WQI of Dinius

Factor 2 (F 2 )
Frequency: It represents the percentage of individual tests that do not meet the objectives ("failed tests"): 2 Number of failed tests 100 Total number of tests

Figure 3 .
Figure 3. Evolution of the development of biotic indices at a global level.
dressed through biota monitoring and represents a response-based monitoring approach.Both approaches have their distinctive features and the ideal course is to use both in an integrated way.As environmental awareness increases and new scientific knowledge about global water quality emerges, the urgency, nature and scopes of the response (R) tend to change data needs, data analysis procedures and data interpretation needs.This makes it necessary to make adoptive changes in the indices, and integrate them into multimetric indices and even multivariate approaches.As a result of events related to climate change, integrated spatial-temporal ecosystem models and indices are useful tools for ecosystem management.Multiple biotic integrity indices based on benthic macroinvertebrates have been developed in different parts of the world.In other regions the water quality is evaluated using the biodiversity indices of this benthic fauna considering relative abundance, Shannon index, Simpson index and Pielou uniformity together with the environmental variables.

Table 1 .
). List of studies carried out in wetlands of Peru, by zone, region and thematic axis.

Table 2 .
Equations for the calculation of global water quality indices considering physical, chemical and biological indicators.
i : Weighted weight for sub-index i.

Table 3 .
Qualifications and weights by parameter included in the INSF water quality index.

Table 4 .
Significance ratings and weights assigned to different parameters in the U-WQI of Boyacioglu.

Table 5 .
Criteria for the assessment of water quality using the BMWP-PeA index, meaning and alert signal.