Sustaining coastal water resources at the intersection of urban planning, biogeochemical sciences and coastal hydrodynamics in the face of sea level rise
Sea level change and sustainability of coastal water resources
Sustaining fresh and saltwater resources in coastal zones in the face of accelerating sea level rise
The tipping point analysis of the impacts of sea level rise on the sustainability of coastal water resources
Sustaining coastal water resources in the face of accelerating sea-level rise
TIPSEACOW Tipping points of sea-level rise and coastal water resources
Sea-level change, thresholds, and coastal water sustainability
Sea-level thresholds for water sustainability
Sea-level thresholds for coastal water sustainability
Sea-level change and thresholds for coastal water sustainability
I. INTRODUCTION
This proposal addresses thecritical question: To what extent are water resources (both fresh and salt) in coastal zones sustainable in the face of accelerating sea level rise? From this question, we develop four specific hypotheses (Section III) to be tested using a work plan (Section IV) that consists of collaborative interdisciplinary field observations, experiments, laboratory analyses, and modelingthat will contribute to broader impacts (Section V)includingdevelopment of an interdisciplinary STEM workforce and contributions to site-specific coastal management.Our question, hypotheses, and work plan arise from results of a Track 1 Coastal SEES planning project (Section II) thatallowed us toassemble thismultidisciplinary teamof PIs with excellent working relationships and communicationabilities.
Our question stems fromuncertaintiesof how sea-level change impacts coastal water resources at various time and spatial scales Uncertainties arise from multiple linked physicochemical, biological and human processes occurring at coastal zones (Fig. 1). These linked processes require interdisciplinary research to respond and adapt tosea-level rise at optimal times,e.g.1, since response and adaptation may become prohibitively expensive or impossible to accomplishonce changing conditions pass certain thresholds (abrupt changes in rates or conditions)2. Our project aims to address severalimportant questions through continued interdisciplinary collaborations initiated with our Coastal SEES Track 1 planning grant. These questions include: What areand how will potential rates of sea-level change impact water resources required by humansand for ecological services? What processes represent thresholds in degradation of water resources? How willcrossing thresholds impact natural and built coastal environments?How do thresholds vary with hydrologic characteristics of coastal aquifers?
II. Results from prior NSF support
A. Martin, Ogram, Peng, Valle-Levinson, OCE-1325227, $441,125, 8/15/2013-7/31/2015 (plus 1-yr no-cost extension),“Coastal SEES (Track 1): Planning for hydrologic and ecological impacts of sea level rise on sustainability of coastal water resources”.
Intellectual merit: This project (hereafter referred to as CS1 for “Coastal SEES Track 1) achieved interdisciplinary field observations, laboratory analyses, and modeling that assessed how sea-level change affectshuman communities, water resources, coastal hydrodynamics, microbial community structures and functions, and biogeochemical reactions at various time scales (Fig. 2). Theprojectfocused on two coastal settings representing end-member subterranean estuaries (STE)3: the east coast of Florida, USA and the east coast of Quintana Roo,Mexico (Yucatan peninsula). Both sites discharge fresh water to coastal lagoons: the Florida STE from a granular, siliciclastic aquifer and the Quitana Roo STE from a carbonate karst aquifer (Fig. 3). These two regions, which have experienced recent rapid population growth,also constitute the field sites for this proposed project (hereafter referred to as CS2 to differentiate it from results derived from CS1).
Our results show that hydrogeology and biogeochemical reactions at both sites depend on aquifer characteristicsand short-term (tidal to decadal) sealevel variations. In the karst region (Quintana Roo), fresh and brackish water dischargevia conduits (water-filled caves), but reversed flow (recharge) occurswhen sea level rises above a threshold of 0.08 m above the average during our fortnightly observation periods (Fig. 4)4. During recharge, oxygen-rich lagoon water flows to the aquifer and catalyzes biogeochemical reactions and during discharge,reaction products, including nutrient-rich water, flows to the lagoon. Switching from discharge to recharge is modulated by wind set up and spring-neap tidal cycles4-6. Biogeochemical reactions reflect changes in microbial community structures(Morrison et al., in review; Bae et al., in press) although understandingcommunity functionsrequires additional samples7. We predict recharge-discharge timing and magnitude will change as water demand,which has risen from 29 to 873 x 106 m3 between 1980 and 2012, increases with population growth (ref?? - Deng and Peng, Chao and Peng in prep??).
In the granular aquifer (Florida), the location of the seepage face (the coastal zone discharging fresh water8) has shifted shoreward by tens of meters as the lagoon flooded following the Last Glacial MaximumLGM9. Data from CS1 extendprevious observations to nearly 10 years and show ~5 m (~25%) shoreward migrationof the seepage face (Fig. 5). We speculate this shoreward shift reflectsacceleration of sea-level rise by about an order of magnitude to rates of ~20 mm/yr over the past 5 years throughout the South Atlantic Bightbased on tide gauge data10.
Biogeochemical reactions are similar at the two study sites including enhanced organic matter remineralization, carbon cycling11, altered nitrogen (N) speciation12, sources of phosphorus (P) from organic matter and carbonate minerals4, reduced metal oxides, sulfate reduction and sulfide oxidation9,13,14, with resulting pH changes, mineral dissolution and changing sources and sinks of P 4. These similarities occur regardless of time and spatial scale differences in STE responses to sea-level change (e.g., Fig. 3), suggesting general results about sea level impacts on coastal zones can be obtained from these sites. Publications[JBM1]: To date, x abstracts7,11,12,15others?), and y papers have been published, submitted or in preparation for the peer-reviewed literature4-6,10Deng and Peng, Chao and Peng in prep. others?).[JBM2]
Broader impacts: CS1 integrated interdisciplinary activity at the University of Florida (UF) centered on coastal water resources and sea level rise. Coupling this project with aUF Water Institute Graduate Fellows (WIGF) Programsupportedthe research of 10 PhD-level graduate students, one post-doctoral researcher, and two additional faculty members. Participants represent five departments (Geological Sciences, Coastal Engineering, Soil and Water Science, Urban and Regional Planning, Wildlife Ecology) and four colleges (Liberal Arts and Sciences; Engineering; Agriculture and Life Sciences; Design, Construction and Planning), reflecting the range of disciplines involved. One of the additional faculty members (Dutton) is aco-PI on this proposal and helped develop it withher prior NSF support (Section IIB).
Our work in Quintana Roo established synergistic activities with Mexican colleagues at CINVESTAV-IPN and Centro de Investigacion Cientifica de Yucatan, in Merida, and at Universidad Nacional Autonoma de Mexico and Parque Nacional Arrecife in Puerto Morelos, including collaborative work with two faculty there and 4 of their graduate students (2 PhD and 2 MS)4,15. Our work in Indian River Lagoonprovides estimates of benthic nutrient fluxes from the STE in support of the St. Johns River Water Management District(one of five Florida water management districts) efforts to prepare a nutrient reduction model to manage harmful algal blooms (HAB).
B. Dutton Sole-PI; EAR[JM3]-1155495, $314,258; 4/1/12 – 5/31/16, “Towards a Global Reconciliation of Last Interglacial Sea Level Observations”
Intellectual Merit: Given the current inability to project dynamic instability of ice sheets under future warming scenarios, the behavior and dynamics of polar ice sheets during past warm periods provide indispensable empirical constraints. This project aims to reconcile observations of the magnitude of peak sea level during the last interglacial period and sea level minima associated with glacials MIS 2 and 6 through fieldwork to survey and collect samples, U-Th dating of corals, and glacial isostatic modeling. Publications: Three papers have appeared in the peer-reviewed literature (refs);another two student-led manuscripts are in prep(refs); at least three more are anticipated; 14 abstracts (6 posters/8 talks, references) presented by the PI and a PhD graduate student at domestic and international conferences.
Broader Impacts: Three graduate students have been supported by the grant, one undergraduate researcher, a class of students participated in collection of field data in the Bahamas, and a video exhibit and a new exhibit on sea level change are being developed in collaboration with the FL Museum of Natural History. The publications in QSR and Science received significant media attention. The Science paper was picked up by more than 25 media outlets globally including Reuters, The Guardian, and The Washington Post. Research from this grant has been featured twice by NSF (on their home page in Jan-2015 and as the top news story for Science360 in July-2015). This media attention directly led to further engagement in public outreach to communicate the research results, including involvement in an upcoming feature film about climate change, as well as a documentary series on climate change being produced by National Geographic (with an episode focused on sea-level rise in south Florida), contributing to an in-depth piece for the New York Times Magazine, and an in-person consultation with US Senator Bill Nelson (D-FL) regarding sea-level rise in Florida.
III. HYPOTHESES AND SIGNIFICANCE
A. Hypotheses to be tested
Hypotheses proposed here center on theoverarching hypothesis that sustainability of coastal water resources depends on rates of sea-level change, consumption and degradation of water resources, biogeochemical transformation at the fresh-salt water interface, and physical connections between fresh and salt water. We breakdown this general hypothesis into specific hypotheses to be tested our interdisciplinary work plan (Section IV), which includes linked and simultaneous observations, experiments, models, and analyses. Results will be jointly reported in peer-reviewed literature and to cognizant water managers. The specific hypotheses and tests include:
Hypothesis 1: Sea-level rise and coastal population growth will degrade coastal water resources at dissimilar spatial and temporal scales. This hypothesis will be tested through comparing extant observations and projections of coastal development and population growth with evaluations of potential rates of sea-level change based sediment archives during the last interglacial period ~125,000 years ago (centennial to millennial rates), observations from tide gauge data (decadal rates), and direct observations(seasonal, storm and tidal scales).
Hypothesis 2:Water resources will degrade abruptly when thresholdsin population densities, sea level, water table elevations, and alterations of microbial communitiesare crossed. This hypothesis will be tested through high-resolution observations of changes in sea level and inland water table at intra-tidal to seasonal time scales; analyses of the impact ofchanging levels on salt and water exchanges between coastal and aquifer water in two end-member types of STEs; measurements of exchange effects on microbial community structures and functions and associated solute (e.g., C, N and P) concentrations; and compiling, modeling, and comparing data related to inland fresh water consumption relative to changes in water table elevations and population growth.
Hypothesis 3: Exceeding thresholdswill alter microbial community structures and functions, nutrient delivery, and salt fluxes, degrade potable water resources, increase cost of human adaptation, and reduce efficacy of adaption measures. This hypothesis will be tested by compiling water resource usage data and measuring water table and sea level vary at seasonal and shorter time scales. These data will becompared with simultaneously measured changes in microbial communities and functions, chemical compositions of water, shifts in hydrodynamic behaviors, and possible contamination from the built environment. These comparisons will be made in the framework of past rates of sea-level change based on sediment archives and projections of future sea level and water usage.
Hypothesis 4: Crossing thresholds depends on hydrologic characteristics of the coastal aquifers comprising the STEs. This hypothesis will be tested by comparing data collected from two distinct STEs, both in a rapidly developing setting. One is composed of granular siliciclastic sediments with diffuse flow in a developed setting and the other is composed of variably lithified carbonate rocks and sediments with conduit flow (Fig. 3).
B. Scientific Significance
Eustatic sea level is rising at ~3.2 mm/yr andprojections suggest that if the rate accelerates as expected, sea level will be0.26 to 1.90 mhigher than now by 210016-18. Rising sea level represents a slow-moving problem, punctuated by short-term disasters (e.g., Hurricanes Katrina and Sandy) for the more than 1 billion people who live along coasts19. Particularly vulnerable areas include densely populated regions of Southeast Asia, Egypt, and sub-Saharan countries20 and the US where ~123 million people (39% of the population) live in coastal counties21. Although attention-grabbing events such as storms, storm surge, flooding, and increased erosion (NRC, 2007) are clear threats, less attention focuses on threats to coastal water resources (both fresh and salt) from rising sea level and increased population, which may limit coastal communities sustainability prior to inundation. Threats to fresh resources include over pumping, waste disposal, and related effects of increasing coastal populations22,23. Threats to salt water resources, which support coastal ecosystems, include changed solute fluxesfrom reduced submarine groundwater discharge (SGD)24,25and altered compositions following reactions caused by salt water intrusion4.
Rates of sea-levelrise vary through time as shown by sea-level reconstructions that span timescales of 10-105 years e.g.26,27 and direct observations based on tide gauges and satellite altimetry16. Sea level rose 3 meterson ecological time scalesbased onspectacular successions of reef faciesat Xcaret in Quintana Roo from the last interglacial28,29. A similar rapid rise is shown by reef exposure surfaces in the Bahamas and Florida, but these sites suggest the rapid rise was preceded by an ephemeral sea level fall of at least 1 meter, reflecting dynamic instability of polar ice sheets during warm climates30,31. Instabilities also appear as meltwater pulses, e.g.32 assea-level rises of 1 to several meters over 102 to 103 yearsduring retreat of Northern Hemisphere ice sheets over the past 20,000 years. The potential for similar rapid sea-level riserates in the future is shown by the recent finding that the West Antarctic ice sheet is susceptible for collapsee.g.33. Understanding potential rates of sea level change is thus critical to develop coping strategies for coastal ecosystems and human communities.
Recent accelerationsof sea-level rise are shown by tide gauge and satellite altimetry data, which reveal a change from a global mean rate of ~1.2-1.9 mm/yr between 1901 and 1990to ~2.8-3.7 mm/yr from 1993-201034. Rates also vary spatially; tide gauge data show ~5 mm/yr rise along the Mid-Atlantic Bight over the past couple of decades35-38. These rates, which are in excess of the global average, reflectwind forcing, deceleration of the Gulf Stream, and changes and/or divergence in the Atlantic Meridional Overturning Circulation (AMOC)39,40,41. Rapid sea level rise also began recently in theSouth Atlantic Bight,with tide gauges showing rates of ~18 mm/yrsince 201110,42. These rates may reflect changes to the Atlantic Multi-decadal Oscillation (AMO)and slowing of the Florida current43,44. Temporal and spatial variations in sea-level riseshould alter biogeochemical processes in STEs and impact sustainability of coastal water resources, depending on hydrodynamic connections between coastal and aquifer waters. Rates of sea-level change and absolute elevationsthus represent important thresholds that when exceeded could permanently degrade coastal water quality.
Subterranean estuaries3 are critical to sustainability of coastal water resources. They receive the first impacts from salt water intrusion as sea level rises23,45 andimpacts will bemodified by changing elevations of the groundwater table46,47Menning et al, 2015). Subterranean estuaries provide a source of ecologically important solutes including nutrients e.g.48,49-51 and metals e.g.52,53,54 to coastal zones. Nutrient fluxes may decreasewithsalt water intrusion or may increase as inland vadose zones shrink, limiting waste disposal options. Salt water intrusion should alter microbial community distributionsand functions in STEs, thereby altering biogeochemical reaction andnutrient fluxes,e.g.51,55-57. Microbial community functions should be affected as dissolved oxygen (DO) and dissolved organic carbon (DOC) concentrations, compositions, origins, and lability11,55,56,58-60. Organic carbon remineralization will alter compositions of the greenhouse gases carbon dioxide (CO2) and methane (CH4), nutrients including N and P, and toxins such as sulfide61. These changes willnegatively impact coastal economies, for example fromdiminished fisheries and tourism, as estuarine water quality degrades. Each of these processes may change abruptly, and possibly permanently, as sea level and water use surpass unknown thresholds.
Human behavior and developmentcan alter natural coastal processes so that a complete understanding of these processes is required to develop predictive models, translate these models to policy, and develop management strategies22. As coastal populations grow and develop coastal lands, water consumption increases even as rising sea level shrinks water availability.Rising sea level and population growth also complicate the ability to treat storm and waste water. Balancing water demand and supply and curbing water demand are critical steps that require an understanding of potential thresholds of sea leveland point to the need for studies that cross boundaries between process-based research of the natural sciences with linkages to human-related investigations of the social sciences. Results of these process-based studies will also have to be interpreted based on past, current, and projected rates of sea level change, whether the rates are accelerating or decelerating, how rates control hydrodynamic and biogeochemical processes, and threshold values.