bioRxiv preprint doi: https://doi.org/10.1101/184101; this version posted September 5, 2017. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 1 Title: From lake to estuary, the tale of two waters. A study of aquatic continuum 2 biogeochemistry. 3 Manuscript Category: Research Article 4 Running Header: River and Estuary Aquatic Continuum 5 6 Paul Julian II1, Eric Milbrandt2, Todd Z. Osborne3,4 7 1 University of Florida, Soil and Water Sciences 8 2199 South Rock Rd, Ft. Pierce, FL 34945 9 ORCID ID: 0000-0002-7617-1354 10 *Corresponding Author: [email protected] 11 12 2 Marine Laboratory, Sanibel Captiva Conservation Foundation, Sanibel, FL 33957 13 Email: [email protected] 14 15 3 University of Florida, Soil and Water Sciences, Gainesville, FL 32611 16 4 University of Florida, Whitney Laboratory for Marine Bioscience, St Augustine, FL 32080 17 Email: [email protected] 18 19 Keywords: Water Management, Aquatic Productivity, Aquatic Continuum, Water Quality, 20 Climate 21 1 bioRxiv preprint doi: https://doi.org/10.1101/184101; this version posted September 5, 2017. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 22 Abstract 23 The balance of fresh and saline water is essential to estuarine ecosystem function. Along the 24 fresh-brackish-saline water gradient within the C-43 canal/Caloosahatchee River estuary (CRE) 25 the quantity, timing and distribution of water and associated water quality significantly 26 influences ecosystem function. Long-term trends of water quality and quantity were assessed 27 from Lake Okeechobee to the CRE between May 1978 to April 2016. Significant changes to 28 monthly flow volumes were detected between the lake and the estuary which correspond to 29 changes in upstream management. and climatic events. Across the 37-year period total 30 phosphorus (TP) flow-weighted mean (FWM) concentration significantly increased at the lake, 31 meanwhile total nitrogen (TN) FMW concentrations significantly declined at both the lake and 32 estuary headwaters. Between May 1999 and April 2016, TN, TP and total organic carbon (TOC), 33 ortho-P and ammonium conditions were assessed within the estuary at several monitoring 34 locations. Generally nutrient concentrations decreased from upstream to downstream with shifts 35 in TN:TP from values >20 in the freshwater portion, ~20 in the estuarine portion and <20 in the 36 marine portion indicating a spatial shift in nutrient limitations along the continuum. Aquatic 37 productivity analysis suggests that the estuary is net heterotrophic with productivity being 38 negatively influenced by TP, TN and TOC likely due to a combination of effects including 39 shading by high color dissolved organic matter. We conclude that rainfall patterns, land use and 40 the resulting discharges of run-off drives the ecology of the C-43/CRE aquatic continuum and 41 associated biogeochemistry rather than water management associated with Lake Okeechobee. 2 bioRxiv preprint doi: https://doi.org/10.1101/184101; this version posted September 5, 2017. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 42 Introduction 43 The aquatic continuum concept (ACC) originated from an ecohydrological concept to understand 44 the transport of material between landscape level patches (i.e. ecosystems) through the aquatic- 45 terrestrial continuum (Jenerette and Lal 2005). Within the literature the ACC is at times 46 synonymous with the river continuum concept (RCC) developed by Vannote et al. (1980), which 47 formulated a conceptual model and framework for characterizing lotic (running water) 48 ecosystems to describe the ecology of communities along a river system. Both the ACC and 49 RCC bridge terrestrial and aquatic biogeochemical processes by shared fundamental concepts 50 such as nutrient limitation, ecosystem nutrient retention and controls of nutrient transitions 51 (Grimm et al. 2003). The one important link between the terrestrial and aquatic ecosystem is the 52 flow of water and energy (England and Rosemond 2004; Abrantes and Sheaves 2010; Mendoza– 53 Lera et al. 2012). Sediment, organic carbon and nutrient loading from land journey through the 54 continuum that includes a path through soils to the open ocean and all compartments between 55 (i.e. groundwater, floodplains, rivers, lakes, estuaries, etc.). The progression of materials and 56 energy through these systems act as a succession of filters in which the hydrology, ecology and 57 biogeochemical processing are tightly coupled and act to retain a significant fraction of the 58 nutrients transported through each system (Bouwman et al. 2013). Retention of nutrients along 59 the aquatic continuum not only influences the total amount of nutrients reaching the aquatic end- 60 member (i.e. ocean) but also how the systems modify the stoichiometry and forms of these 61 nutrients en-route (Billen 1993; Reddy et al. 1999; Ensign and Doyle 2006). However, 62 anthropogenic alteration of the ecosystem has changed the hydrology and nutrient stoichiometry 63 and forms along the aquatic continuum. 3 bioRxiv preprint doi: https://doi.org/10.1101/184101; this version posted September 5, 2017. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 64 Primary production forms a critical base to estuarine food webs, strongly influencing oxygen and 65 nutrient dynamics (Caffrey et al. 2013). The magnitude and relative values of gross primary 66 productivity (GPP) and ecosystem respiration (ER) can vary due to flow (stagnant versus 67 flowing conditions), inputs of terrestrial or anthropogenic organic carbon (OC) and nutrients 68 (Odum 1956). Organic matter (OM) in river and estuarine systems are principally derived from 69 terrestrial vegetation and soils, considered recalcitrant and transported conservatively to the 70 ocean. However, several biogeochemical processes can contribute to non-conservative behavior 71 of OM in estuarine ecosystems (Bianchi 2013). Nutrients enter estuaries from either terrestrial 72 sources via run-off, upstream from freshwater rivers and wetlands or tidal exchange of marine 73 waters and in some areas, terrestrial inputs of nutrients have had deleterious effects on estuarine 74 and coastal ecosystems (Jickells 1998; Bianchi 2013). Hydrologic pulsing of freshwater and the 75 associated delivery of OC and nutrients have been observed to influence net aquatic productivity 76 in river, wetland and coastal wetland ecosystems (Gallardo et al. 2012; Maynard et al. 2012; 77 Shen et al. 2015). 78 Inflow of freshwater to an estuary is a significant landscape process that shapes community 79 structure (Mannino and Montagna 1997). The management of freshwater inflows to estuaries can 80 have profound effects on conditions and ecosystem function (Sklar and Browder 1998; 81 Kimmerer 2002; Alber 2002). Similar to many urbanized coastal areas, south Florida estuaries 82 have been significantly altered (Macauley et al. 2002). Along with the loss of shoreline habitat 83 and function, the draining and channelization of wetlands for the purposes of agriculture and 84 diversion of water for urban development has led to increased wet season flows and decreased 85 dry season flows (Doering and Chamberlain 1999). This change in flow patterns has changed 86 the distribution and abundance of key estuarine indicator species such as seagrasses and oysters 4 bioRxiv preprint doi: https://doi.org/10.1101/184101; this version posted September 5, 2017. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 87 (Buzzelli et al. 2015). Oysters are sensitive to salinity and siltation (Barnes et al. 2007; Soniat et 88 al. 2013) while salinity patterns also influence the composition, distribution and abundance of 89 seagrass habitats in estuarine ecosystems (Livingston et al. 1998; Doering et al. 2002; 90 Greenawalt-Boswell et al. 2006). Unlike other estuaries, artificial connections to Lake 91 Okeechobee create the potential for transport of material to the Caloosahatchee and St. Lucie 92 Estuaries from an expanded drainage area extending to the chain of lakes near Orlando, a 93 distance of over 300 km. In combination with alterations to the local watersheds of both systems 94 (Doering et al. 2006; Wan et al. 2014; Sun et al. 2016), this connection has resulted in significant 95 alteration to the timing, distribution and volume of water entering these estuaries. 96 The completion of the Lake Okeechobee levy in 1937 brought the loss of connectivity with the 97 Florida Everglades and reduced its total area by 50% (Steinman et al. 2002) and ultimately 98 disrupting the aquatic continuum. Loss of the Everglades connection also resulted in the loss of 99 significant amounts of water storage and simultaneously increased nutrient loading to the 100 Caloosahatchee and St. Lucie estuaries. While much attention has been directed at Florida Bay, 101 the coral reefs of the Florida Keys and the Everglades wetlands downstream of Lake Okeechobee 102 (Porter and Porter 2002), the conditions within the Caloosahatchee and St. Lucie Estuaries are 103 dictated by base flows, local basin stormwater runoff and regulatory releases from Lake 104 Okeechobee (Doering and Chamberlain 1999; Chamberlain and Hayward 1996). Two major 105 problems for the Caloosahatchee River Estuary (CRE) are excessive nutrient loading and high 106 frequency and duration of undesirable salinity ranges within the estuary (Barnes 2005; South 107 Florida Water Management District et al. 2009). 108 This study had three objectives to contrast the ecological and biogeochemical processes across 109 the aquatic continuum. The first objective was to evaluate changes in water quality and quantity 5 bioRxiv preprint doi: https://doi.org/10.1101/184101; this version posted September 5, 2017.