Environmental impacts on lake Azué௠in Haiti due to degradation of its watershed

4 IV. Results

The results reported in the table below are coming from several different sources and some of them are old. However, they give an idea about the operating status of the lake in the past. But the exception is made for those produced by Christian, et al. (2011). They can provide information on current ecology of the lake.

Table II: The water quality measurements for the Lake Azuei

A. Physical Parameters	Data available	References
1. Water Clarity or Transparency	Average Secchi^3(*) depth : 3.25 m	Christian, Dorval and Hannigan, 2011
2. Dissolved Oxygen	6.2-8.6 mg/L	US Army Corps of Engineers, 1999
3. Temperature	27-30.5 (28,75) ^OC	US Army Corps of Engineers, 1999
B. Chemical Parameters
1. Phosphorus	10.58 (#177; 13.82) ug/L	Christian, Dorval and Hannigan, 2011
2. Nitrogen	419.02 (#177;19.31 SD) ug/L	Christian, Dorval and Hannigan, 2011
4. Total Dissolved Solids (TSS)	7,500 to 10,650 mg/L	US Army Corps of Engineers, 1999
5. Hardness	525-2260 mg/L	Matthes, 1988
6. pH	7.5-8.1 (8.5)	Matthes, 1988
7. Alkalinity	195 - 490 mg/L	Matthes, 1988
8. Salinity	6.92 - 15.53 ( ppt)	Matthes, 1988
9. Conductivity	500-600 umhos/cm	Matthes, 1988
C. Biological Parameters
1. Chlorophyll a	2.39 (#177; 0.39 SD) ug/L	Christian, Dorval and Hannigan, 2011
Color of Water ( Code Forel)	greenish-40% (phytoplancton)	Matthes, 1988

The fish kill in Lake Azuei is the result of a series of biophysicochemical transformations in the lake environment (Table II). This transformation of natural or anthropogenic causes inevitably the death of the lake, due to inputs of sediments and nutrients. At first glance, this event is caused by the phenomenon of eutrophication of the lake. The mineral nutrients such as nitrogen, phosphorus, etc., depending on their concentration, operate in the equilibrium with the environment.

These elements are essential to plants, but a drastic increase in their concentration causes massive growth of algae and aquatic plants. An eutrophic aquatic environment is an environment rich in nutrients and with high productivity (Hade, 2002). These processes result in the change of the pH and the reduction of oxygen in the lake which is the origin of death of fishes into the lake.

Table III: Classification of Lakes concerning the trophic level based on OECD (1982)

Trophic Level	Phosphorus	ChlorophyllA	Transparence
Oligotrophic	< 10 mg/m3	< 2.5 mg/m3	6m-12m
Mesotrophic	10-35 mg/m3	2.5-8 mg/m3	3m-6m
Eutrotrophic	35-100 mg/m3	8-25 mg/m3	3m-1.5m
Hypertrophic	> 100 mg/m3	> 25 mg/m3	< 1.5m
Organisation for Economic Cooperation and Development (OECD, 1982)

These data were (Table III) collected by Christian et al. (2011 from some samples collected in the lake, we think they can help to understand what are happened in the ecological processes of the lake.

Euthrophic: Refers to a water body shallow and turbid where an excessive concentration of plant nutrients causes algal blooms.
Oligotrophic: refers to water clear, deep and low in nutrients. There is little organic matter and a high content of dissolved oxygen.
Mesotrophic: Refers to a lake enriched by nutrients, with an early accumulation of sediments and organic matter, which the water is slightly turbid with a reduction of the dissolved oxygen at depth. Biological productivity increases and is manifested by the installation of aquatic plants, an increased presence of algae. Changes in fish community appear.

Enviromental impacts on Lake Azuei:

Based on the OECD fixed boundary classification scheme, we classified Lake Azuei as mesotrophic. Secchi depth indicated euthrophic; chlorophyll indicated oligotrophic; and phosphorus and nitrogen indicated mesotrophic. But we can consider there is a tendency to an ecological disruption in Lake Azuei by providing nutrients to the process of erosion as the surrounding mountains of the lake are highly degraded. In this case, additional studies will be necessary to understand more on the biological functioning of Lake Azuei.

* 1 N.B: A Secchi disk is a device for measuring the transparency of a body of water. It consists of a disc of about twenty centimeters, black and white (each quarter turn). The disc is attached to end of a cord and weighted, is left down to disappearance then there is the length of the rope. Then hauled the rope up there and then reappear the length of the rope. The depth of the Secchi disk is the midpoint between the two measures. Retrieved october 30, 2011 from www.wikipedia.com .