Plankton biodiversity, water quality and environmental status of Los Baños' Crocodile Lake and San Pablo City's seven lakes (Lakes Sampaloc and Pandin) [Philippines]

The limnological findings indicate that Lake Pandin is the most pristine of the three bodies of water. It manifested highly significant temporal variations based on the physical parameters used. Only the SDT and DO [dissolved oxygen] differentiated the sampling station from each other to a highly significant degree. Lake Pandin manifested the full range of trophic states from the oligotrophic (nutrient poor, low in algal biomass and fish biomass also). It is a relatively cool lake (mean water temperature = 26.5 deg C), with an alkaline pH (pH 7.3), and a mean DO content of 8.7 mg/L (80% DO saturation). The lake vacillates between the moderately hard to very hard water categories based on the classification by the APHA (1992), is rich in ammonia (mean = 0.216 mg/L) that has a tendency to spike in the mid-lake region. Elevated concentrations of NH3-N develop during a lake turn-over which, in this study take place in January. Nitrate-N is significantly reduced when the ammonia-N increases. Ammonia-N is the most significant contributor to the fluctuating TIN [total inorganic nitrogen] in the lake. The TIN levels become maximal during an algal bloom, indicative of the phytoplankton being an important source of N enrichment of the lake. Soluble reactive phosphorus is highest in the lake during a lake overturn, evidence that the P supply in the opilimnion comes from the sediment pool at the lake bottom in the sediments. The TP [total phosphorus] of the lake is low for the most part of the year but starts getting replenished during the lake overturn and reaches peak levels during an algal bloom. Chlorophyll a in the lake is low (1-4 microgram/l) for the most part of the year relegating this body of water to the oligotrophic category for the same length of time. Then it becomes eutrophic during the summer algal bloom. The intensity of the summer eutrophication is suspected to be dependent on the intensity of the lake overturn. The amount of nutrient enrichment from the overturn is dependent on cultural eutrophication, and the amount of protection people give their lake. A total of 77 species were identified in Lake Pandin alone distributed among the algal classes as follows: Cyanophyceae, Chlorophyceae, Chrysophyceae, Dinophyceae and Bacillariophyceae. Species diversity in the phytoplankton ranged from 01.6 to 1.87 (June 2008-March 2009). The diversity index increased during the lake turnover because algae that were lying dormant at the lake bottom were re-suspended during this phenomenon. The bloom-forming algal species in the lake were Microcyses aeruginosa and Ceratium sp. Sampalok Lake is a turbid lake with a secchi disk transparency mean of 1.3 m. Based on the mean water temperature, it is slightly warmer than Pandin Lake, reaching a slightly higher maximum. Average wise, it is relatively less aerated and with a slightly higher mean pH than Pandin. It had a higher total alkalinity indicative of a higher potential productivity. Its higher levels of EC [electrical conductivity] implies a relatively higher fertility which was evident in its higher ammonia, nitrite and nitrate means. Its mean TIN [total inorganic nitrogen] concentration was more than three times that observed in Pandin. Pandin's SRP [Soluble Reactive Phosphorus] never exceeded 1 mg/L, but that of Sampaloc had a mean of 1.1 mg/L, indicative of this lake's high potential for algal production that would benefit the fish that feed on them. The TP mean of 1.4 mg/L was five times that of L. Pandin. While L. Pandin exceeded the recommended level of COD for the prevention of extreme pollution, the exceedance by L. Sampaloc was almost three times the excess of L. Pandin. Chl a mean was indicative of eutrophication. In only two instances was Chl a found indicative of mesotrophy: a total of 38 species of algae were identified which is roughly 49% that observed in Lake Pandin. Sampaloc L. is more disturbed than the smaller lake which belongs to the oligotrophic category. Crocodile Lake is as turbid as Sampaloc Lake, its SDT down to a mean of 1.1 m only. It is warmer than Sampaloc Lake, by roughly 1 deg C. It tends to be less aerated than Sampaloc Lake but with a similar pH. Crocodile Lake is highly alkaline, its total alkalinity more than twice that of L. Sampaloc. Its EC is more than three times higher but is similarly of moderately hard water category. Ammonia-N is highest in this lake with the nitrate-N higher than L. Sampaloc but lower that that of L. Pandin. Its total nitrogen is twice that of the big lake, but in the overall, L. Crocodile is N-limited based on the 1:1 ratio of the TIP and TP. Both L. Sampaloc and Crocodile are eutrophic and organically polluted. The Chl a of the big lake was not equalled by Crocodile L implying that the latter was seemingly less disturbed. This relatively smaller number of species of algae found in the bigger lake tends to show that the relatively more disturbed state of the bigger lake had an adverse effect on algal species diversity. There were only 42 species of algae identified which is roughly 55% that found in L. Pandin. Reduction of algal species diversity stems from the increased tendency for some species to become dominant.