On the morning of September 19, 2017, around 11:20, a diver in Lake Jackson, Florida, fed a hose approximately 6.7 meters down to the throat of a lake-bottom sinkhole known as Porter Hole Sink and, over about six and a half minutes, injected 45.4 kilograms of 20 percent Rhodamine WT into the hole. Thirty-five days later, instruments located 30.6 kilometers \u2014 around 19 miles \u2014 to the south detected that same dye emerging from the vent at Wakulla Spring. The trace, published in the Journal of Cave and Karst Studies by Se\u00e1n E. McGlynn and Alan W. Niedoroda, represents one of the longer confirmed conduit pathways documented in the Upper Floridan aquifer, and its most intriguing detail might not be the distance itself. It could be the minimal amount of pink dye that ever reappeared.<\/p>\n
## A lake with a drain in the bottom<\/p>\n
Lake Jackson rests north of Tallahassee in an environment that functions less like a watershed and more like a plumbing diagram. The limestone below is filled with dissolution features, and the lake periodically illustrates this by draining itself. Porter Hole Sink is one of the openings responsible: a sinkhole in the lake bed that, when the sediment plug above it loosens, allows water to flow directly into the aquifer below. There is no stream carrying that water away, no surface channel to monitor. The water simply exits through the bottom.<\/p>\n
This is the practical issue that karst hydrogeology aims to address. In a typical drainage basin, one can stand at a confluence and observe the flow. In carbonate regions, the flow paths are buried, irregular, and often counterintuitive \u2014 conduits can traverse beneath surface divides, split, merge, and channel water to springs that no topographic map would indicate. The only method to identify where a sink leads is to inject something distinctive into it and monitor downstream with an instrument sensitive enough to detect it.<\/p>\n
Rhodamine WT is the typical choice. It is a fluorescent tracer dye, vividly pink in the container and effectively invisible once it has passed through the aquifer, detectable by fluorometry at concentrations measured in micrograms per liter. It travels with the water rather than adhering to rock, which is what renders it useful, and it is employed frequently enough that state agencies issue public notices when a trace is occurring so that no one panics at a discolored ditch. Injecting it into a lake-bottom sinkhole instead of a well is the more challenging version of the task: the dye enters at depth, in a lake, and whatever occurs next happens in obscurity.<\/p>\n
## Thirty-five days, and a sonde that noticed<\/p>\n
Wakulla Spring is a first-magnitude spring \u2014 the premier discharge category \u2014 and the highlight of Edward Ball Wakulla Springs State Park, where the water flows through one of the most thoroughly mapped underwater cave systems globally. It is also the prime site to observe any substance injected into the Tallahassee karst, and in 2017 it was equipped with instruments for exactly that purpose.<\/p>\n
The signal arrived on October 24, 2017, approximately 35 days post-injection: a coherent dye peak at Wakulla Spring detected by sondes rather than visually. Nothing about the spring appeared different to visitors. The dye had been diluted through dozens of kilometers of limestone into the microgram-per-liter range, a concentration resolvable by a fluorometer but unnoticeable to the human eye. This is important to clarify because the alternative image is more entertaining yet entirely inaccurate: there was no pink spring, no tinted glass-bottom boat ride. There was a curve on a graph, and the curve had a shape consistent with a single slug of tracer that had been traveling for a month.<\/p>\n
Sally Ward Spring, located nearby, generated its own coherent peak around the same 35-day interval, with initial faint signals appearing around day 31. Charcoal packs placed at other nearby springs also detected dye, indicating a conduit network that weaves and diverges rather than functioning as a single pipeline from sink to spring. Averaging across the period, the plume moved at a rate of approximately 0.8 to 0.87 kilometers per day \u2014 swift for groundwater, exceedingly slow for anything with a current.<\/p>\n
## The dye that never came back<\/p>\n
The finding that the authors approach with the most caution is the accounting. Very little of the 45.4 kilograms injected at Porter Hole Sink was recovered at Wakulla Spring. The vast majority of the tracer seems to have dispersed into the limestone structure \u2014 the fine porosity and small fractures adjacent to the conduits \u2014 instead of remaining in the fast-flow channel until it reached the vent. The paper clearly states that this mass balance is exploratory and somewhat conjectural; it is impossible to instrument every outlet in a karst system, and dye that permeates the matrix<\/p>\n","protected":false},"excerpt":{"rendered":"
On the morning of September 19, 2017, around 11:20, a diver in Lake Jackson, Florida, fed a hose approximately 6.7 meters down to the throat of a lake-bottom sinkhole known as Porter Hole Sink and, over about six and a half minutes, injected 45.4 kilograms of 20 percent Rhodamine WT into the hole. Thirty-five days […]<\/p>\n","protected":false},"author":2,"featured_media":375938,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"Default","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[179],"class_list":["post-375937","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized","tag-source-scienceblog-com"],"_links":{"self":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/posts\/375937","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=375937"}],"version-history":[{"count":0,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/posts\/375937\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=\/wp\/v2\/media\/375938"}],"wp:attachment":[{"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=375937"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=375937"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wolfscientific.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=375937"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}