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Eight (8) human-induced stressors were identified in the seven lakes, as shown below. Each lake has its own historical account of these stressors based on the Focus Group Discussion (FGD) conducted among lake communities.
Introduction of Invasive species
Non-collection of solid waste
Violation of the 10% limit of fish cages
Use of sinker feeds
Application of inorganic fertilizers
Improper discharge of liquid waste
Improper solid waste disposal
Quarrying
A problem tree analysis was conducted for the lakes, which results are presented below:
The Seven Lakes Problem Tree of All Identified Stressors
The major causes of the problem tree can be summarized into three: poor enforcement of the law, which directly affects the water quality due to uncontrolled dumping of wastes, increase in business and residential areas within the poor monitoring of the activities, and wanting institutional capacity to enforce policies. These have significantly affected the lake's major use- that is, for fishery and tourism. The inability to address the problem's causes led to further lake degradation.
As of 2023, all seven lakes have achieved the 10% aquaculture carrying capacity based on the LLDA and San Pablo LGU data of registered fish cages for the year. However, unregistered fish cages in lakes Palakpakin, Bunot, and Calibato remain challenging for regulating authorities. Aside from unregistered fish cages, the seven lakes also face other human-induced stressors, such as improper disposal of solid wastes and improper discharge of wastewater.
However, achieving the 10% aquaculture carrying capacity does not mean that the recommended stocking density, feeding requirements, and spacing of fish cages are followed since LLDA, BFAR, and the LGU cannot monitor these practices yet. The recommended stocking density of the San Pablo LGU is 3,500 for every 10m x 10m x 5 m cage and a feeding volume of 56 bags for an expected feed conversion ratio (FCR) of 1.5.
Meanwhile, the recommended spacing between cages is 5-10m, and the distance between is 30-50m, as stated in LLDA MC 2017-03. Overstocking and not following the recommended spacing for fish cages can cause isolated fish kill scenarios. Overfeeding, on the other hand, and the long-term use of sinker feeds, the leftovers that sink to the bottom of the lake, can contribute to the oversaturation of nutrients such as phosphorus in the water eutrophic.
The Historical Accounts of Human-Induced Stressors on Each Lake
Click on the links of each lake to see data and insights.
The Water Quality: Lake Health Indicators
Water quality is the primary indicator to check lake health. The Laguna Lake Development Authority (LLDA) regularly monitors the parameters shown below. Click on each icon to read the description of each parameter. (Descriptions source: LLDA Water Quality Report 2006-2008; source for Chemical Oxygen Demand: Z. Hu, D. Grasso, in Encyclopedia of Analytical Science (Second Edition), 2005).
BOD is a measure of how much oxygen is used by microorganism in the aerobic oxidation, or breakdown of organic matter in the streams. Usually, the higher the amount of organic matter found in the stream, the more oxygen is used for aerobic oxidation. The higher the BOD, the more polluted the water.
Chloride anions are usually present in natural waters. A high chloride concentration is evident in water that is in contact with rock formation. It can also indicate sewage and industrial pollution or an intrusion of salt water into a freshwater body. A high chloride content has a corrosive effect on metal pipes and structures and harms most trees and plants.
COD is often used to measure water pollutants, wastewater, and aqueous hazardous wastes. High level of COD lowers Dissolved Oxygen.
Dissolved Oxygen is a very important indicator of a water body’s ability to support aquatic life. It is found in microscopic bubbles of oxygen that are mixed in the water and occurs between water molecules. Oxygen enters the water by absorption directly from the atmosphere or by aquatic plant and algae photosynthesis. Oxygen is removed from the water by respiration and decomposition of organic matter. The colder the water, the more oxygen can be dissolved in water. In general, as water temperature increases, dissolved oxygen decreases. Freshwater lakes, streams, and tap water generally contain much less salt, so dissolved oxygen are higher.
Phosphate is found in fertilizers and some detergents. Phosphorus is necessary for plant and animal growth. Too much production of these nutrients leads to eutrophication.
The term “pH” was originally derived from the French term “pouvoir hydrogene”; in English, this means “hydrogen power.” pH is a measure of the acidity or alkalinity of water. It is usually measured by a colorimetric test - litmus paper which changes color with increased acidity or alkalinity or by electrometric method - pH meter. The pH scale ranges from 0 to 14. If the water is acidic, the pH is 0 to 6.9; neutral is 7.0; alkaline is 7.1 to 14. A pH range of 6.5 to 8 is optimal for freshwater.
Total Dissolved Solids are solids in water that can pass through a filter. These maybe anions and cations, such as carbonate, bicarbonate, calcium, magnesium, which are necessary for aquatic life. High TDS concentrations can produce laxative effect and can give unpleasant mineral taste to water.
Total Suspended Solids are solids in water that can be trapped by a filter. TSS can include silt, decaying plants, animal matter, industrial waste and sewage. High concentration of suspended solids can cause many problems for stream health and aquatic life.
The coliform group is used as an indicator of the sanitary quality of the water because its presence in the water body would suggest fecal contamination or would indicate the disease-producing potential of the water. Ideally, water should not contain any microorganisms known to be pathogenic or any bacteria indicative of fecal pollution. In order to estimate the probability of the pathogens being contributed from human feces as well as from animal droppings, the total coliform and fecal coliform must be quantified. High counts of coliform bacteria will render the water unsuitable for domestic water supply, fishery, agricultural, recreational and some industrial uses.
A contributory factor to the accumulation of nutrients, thus the deoxygenation of the water, is the improper drainage of wastewater by residential and commercial establishments within the easement and near the lake and the improper disposal of solid wastes through leachate by residents, businesses, and tourists. Wastewater discharge can contain microorganisms oxidizing reduced substances, measured by the biochemical oxygen demand (BOD). The higher the BOD, the less oxygen is available for the fish (Bhateria and Jain, 2016). Among the seven lakes, Bunot Lake has the highest average BOD levels for most of the years from 1996 to 2018
According to Vasistha (2020), DO is an accurate indicator of pollution since the level of DO decreases along with the increase in the temperature of water and changes in color, taste, and odor. The level of DO dictates the capacity of a lake to support aquatic life. The chart above shows that the seven lakes consistently passed the average DO levels for a Class C water body from 2009 to 2018.
The red bar and line represent the accepted level of phosphate for a Class C waterbody based on DAO 2016-08. The average phosphate levels in Sampaloc and Calibato have always exceeded the accepted phosphate level of 0.5 milligrams per liter (mg/L). Aside from phosphates, commercial feeds and fish wastes can also contain nitrates, other chemical pollutants, and by-products of metabolism, such as ammonia.
Nutrients like phosphorus and nitrogen are vital to the growth of fish and the freshwater ecosystem in general. Still, excessive amounts can result in eutrophication that increases the decomposition rate, which requires oxygen (Paller et al., 2021). Also, eutrophic lakes encourage the growth of many aquatic plants or algae (Bhateria and Jain, 2016). The excessive growth of water lilies and algae can further reduce oxygen levels in the water and eventually result in fish kills. Water lilies still proliferate in Sampaloc and Calibato lakes. In contrast, Palakpakin is proliferated with water lilies and algae despite regular lake cleanup activities by the FARMC and Bantay Lawa.
TSS can be composed of silt, decaying plants, animal matters, industrial wastes, and sewage (LLDA, 2012). Figure 27 graphs the average TSS levels on the seven lakes from 1996-2018. According to Akan (2012), soil erosion is the primary cause of TSS, but human activities add to the concentration of TSS in the water. High TSS concentrations can increase water temperature, reduce oxygen, cause injuries to fish, clog the gills and respiratory passage of fish, and decrease the photosynthetic activity of aquatic plants that serve as food to some aquatic life. Further, particles that sink to the bottom trap bacteria that make the water anoxic or hypoxic in that part of the lake. As seen on the Figure, the average TSS levels on the seven lakes from 1996-2018 are below the threshold for a Class C waterbody, except for Sampaloc in 2005.
Water Quality Data Source: Laguna Lake Development Authority
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