Deliz-Quiñonez, Katherine Y.

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    Water quality assessment of a tropical freshwater marsh using aquatic insects
    (2005) Deliz-Quiñonez, Katherine Y.; Santos-Flores, Carlos J.; College of Arts and Sciences - Sciences; Massol Deyá, Arturo; Acosta Martínez, Jaime; Department of Biology; Alston, Dallas
    Laguna Cartagena, located in the municipality of Lajas, is the only natural freshwater lagoon of Puerto Rico. The lagoon gives refuge to many animal and plant species, some of them endemic and endangered. Agriculture in contiguous lands has caused sedimentation and eutrophication, affecting not only its hydrology but its capacity to sustain a high diversity of aquatic life. To restore the Lagoon, its actual condition was assessed based on the physical-chemical (pH, temperature, dissolved oxygen (DO), nutrients and heavy metals) and biological characteristics (aquatic insects) of two sites on the southwestern section of the lagoon. A total of 67 insect species in 33 families were collected; 48 of them were new records for the lagoon. Insects belonged to five different orders Hemiptera, Diptera, Coleoptera, Odonata, and Ephemeroptera. Hemiptera and Diptera were the most abundant orders, exceeding 75% of the overall sample. Meanwhile, Coleoptera (21 species), Odonata (17 species), and Hemiptera (16 species) were the orders with higher species diversity, although represented mainly by a few dominant families. Ephemeroptera was the least abundant and diverse order, represented by one species of the family Baetidae. Abundance and diversity was related mainly to DO concentration. According to Simpson and Shannon-Wiener biotic indexes, both sites (1 and 2) showed a higher diversity during February and March. The Hutchinson t-test for Shannon – Wiener shows a significant difference of aquatic insect diversity between the two study sites. Among physical-chemical parameters measured at the lagoon, only DO and depth had significant fluctuations, meanwhile temperature and pH remained within acceptable ranges for the Puerto Rico Environmental Quality Board (PREQB). Ammonia and phosphate were 60 and 7 times, respectively, above those permitted by the PREQB. According to PREQB and EPA, reported values of heavy metal are not toxic to aquatic life. Chemical data indicate Laguna Cartagena has moderate water quality while biological data indicate the lagoon has a fair water quality. Laguna Cartagena is a constantly changing environment. During the year of sampling the lagoon had variable physical-chemical parameters, vegetation and insect community; however, the variability was similar to those wetlands of eastern USA. Further long-term studies should be done to understand better and predict the hydrological changes and population dynamics of the lagoon.