Water quality in The Lachuá Ecoregion Landscape: Comparing streams from Forest, Milpa, and an Oil Palm plantation

Abstract

The hydrological network in the Lachuá Ecoregion (EL), Alta Verapaz, Guatemala, hosts high levels of biodiversity and supplies water to 44 Mayan communities. Despite this critical fact, this network has been threatened by scarcely monitored industrial activities including the rapidly expanding oil palm monoculture (Elaeis guineensis Jacq). Regardless of Lachua’s freshwaters importance, there is little information on how this monoculture impacts them. We compared water-quality properties from streams in oil palm plantations (P), paddock and milpa systems (M), and primary forests (F) in EL. During 2015-2016, 13 rivers were sampled (5 times) for water temperature, pH, dissolved oxygen (DO), conductivity, hardness, chemical and biochemical oxygen demand (COD and BOD), and concentration of silica, nitrates, phosphates, and ammonia. Several parameters showed significant differences. P were 2.7ºC and 1.8ºC warmer than M and F and carried 1.4mg/L more nitrates than F. F carried 10.8mg/L and 11.8mg/L more silica than M and P. M showed intermediate temperatures and silica concentrations, as well as 14.8µS/cm and 8.9µS/cm lower conductivities than P and F. Additionally, COD in M was 9.9mg/L and 4.6mg/L lower than P and F. We believe higher temperatures and lower silica in P are due to the loss of riparian forest and their role in buffering temperatures and recycling silicon. In addition, the existence of secondary forest (guamil) in M might explain the intermediate temperatures and silica concentrations. Our results highlight the contributions of forests to waterways and suggest potential water-quality depletion from the oil palm expansion in EL.